U.S. patent application number 17/052922 was filed with the patent office on 2021-07-29 for strain element, strain element manufacturing method, and physical quantity measuring sensor.
This patent application is currently assigned to SINTOKOGIO, LTD.. The applicant listed for this patent is SINTOKOGIO, LTD.. Invention is credited to Hiroyasu MAKINO, Masahiko NAGASAKA.
Application Number | 20210231514 17/052922 |
Document ID | / |
Family ID | 1000005539874 |
Filed Date | 2021-07-29 |
United States Patent
Application |
20210231514 |
Kind Code |
A1 |
NAGASAKA; Masahiko ; et
al. |
July 29, 2021 |
STRAIN ELEMENT, STRAIN ELEMENT MANUFACTURING METHOD, AND PHYSICAL
QUANTITY MEASURING SENSOR
Abstract
A strain element (10), which is configured such that a frame
portion (11) and a central portion (12) are connected by arm
portions (20) to (22), is masked except for the arm portions (20)
to (22) where a strain gauge (A1) and the like are to be disposed,
and then peening is carried out. With this, a compressive residual
stress layer is formed on four sides of each of the arm portions
(20) to (22). When the strain element (10) receives a load
resulting from an external force, the arm portions (20) to (22)
elastically deform; however, due to the compressive residual stress
layer thus formed, the arm portions (20) to (22) are less prone to
fatigue failure. When projection of a shot material is carried out
as peening, the surface roughness of the arm portions (20) to (22)
increases, the adhesion of strain gauges improves, detection
accuracy improves, and stable measurement can be ensured.
Inventors: |
NAGASAKA; Masahiko; (Aichi,
JP) ; MAKINO; Hiroyasu; (Aichi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SINTOKOGIO, LTD. |
Nagoya-shi, Aichi |
|
JP |
|
|
Assignee: |
SINTOKOGIO, LTD.
Nagoya-shi, Aichi
JP
|
Family ID: |
1000005539874 |
Appl. No.: |
17/052922 |
Filed: |
June 3, 2019 |
PCT Filed: |
June 3, 2019 |
PCT NO: |
PCT/JP2019/021940 |
371 Date: |
November 4, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B24C 1/10 20130101; G01L
1/2287 20130101; G01L 5/1627 20200101 |
International
Class: |
G01L 5/1627 20060101
G01L005/1627; G01L 1/22 20060101 G01L001/22 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 14, 2018 |
JP |
2018-113889 |
Claims
1. A strain element which is elastically deformable in response to
a load and which is configured to have a strain gauge disposed
thereon, the strain gauge being configured to carry out detection
of strain associated with deformation, the strain element
comprising a strain portion which corresponds to a region subject
to strain and which includes an area for disposition of the strain
gauge, the strain portion being provided with a residual stress
layer having negative residual stress.
2. The strain element according to claim 1, wherein the strain
portion has a surface roughness rougher than a portion other than
the strain portion.
3. The strain element according to claim 1, comprising: a frame
portion; a central portion which is located in a space defined by
the frame portion so as to be spaced apart from the frame portion;
and an arm portion which connects the frame portion with the
central portion and which is included in the strain portion,
wherein the frame portion has a first through-opening in a junction
where the frame portion connects to the arm portion, the arm
portion has, disposed on one face thereof, four of the strain
gauges consisting of a first strain gauge, a second strain gauge, a
third strain gauge, and a fourth strain gauge, the first strain
gauge and the second strain gauge are disposed in an area close to
the central portion such that (i) the first strain gauge and the
second strain gauge are symmetrical to each other with respect to a
center line of the one face, the center line extending in a
direction of extension of the arm portion, and (ii) detection
directions of the first strain gauge and the second strain gauge
are parallel to the center line, and the third strain gauge and the
fourth strain gauge are disposed in an area close to the frame
portion such that (i) the third strain gauge and the fourth strain
gauge are symmetrical to each other with respect to the center line
and (ii) detection directions of the third strain gauge and the
fourth strain gauge are at an angle to the center line so as to
diverge away from each other with decreasing distance to the
central portion.
4. The strain element according to claim 1, comprising: a frame
portion; a central portion which is located in a space defined by
the frame portion so as to be spaced apart from the frame portion;
and an arm portion which connects the frame portion with the
central portion and which is included in the strain portion,
wherein the central portion has (i) a locating through-hole in an
area corresponding to an extension of the arm portion and (ii) a
second through-opening located between the locating through-hole
and a junction where the central portion connects to the arm
portion.
5. A method of producing a strain element which is elastically
deformable in response to a load and which is configured to have a
strain gauge disposed thereon, the strain gauge being configured to
carry out detection of strain associated with deformation, the
method comprising the steps of: a) masking the strain element
except for a strain portion which corresponds to a region subject
to strain and which includes an area for disposition of the strain
gauge; and b) projecting a shot material at the strain element
which has been masked, the step b) including causing the shot
material to collide with the strain portion and thereby producing
the strain element in which the strain portion is provided with a
residual stress layer having negative residual stress and in which
the strain portion has a surface roughness rougher than a portion
other than the strain portion.
6. The method according to claim 5, wherein the strain element
includes (i) a frame portion, (ii) a central portion which is
located in a space defined by the frame portion so as to be spaced
apart from the frame portion, and (iii) an arm portion which
connects the frame portion with the central portion and which is
included in the strain portion, the method comprising the step of
corner easing comprising easing (i) a corner of an edge of a
junction where the frame portion and the arm portion connect to
each other or (ii) a corner of an edge of a junction where the
central portion and the arm portion connect to each other.
7. A physical quantity measurement sensor comprising a strain
element according to claim 1, the physical quantity measurement
sensor being configured to measure a physical quantity
corresponding to deformation of the strain element in response to a
load.
8. A physical quantity measurement sensor comprising a strain
element produced by a method according to claim 5, the physical
quantity measurement sensor being configured to measure a physical
quantity corresponding to deformation of the strain element in
response to a load.
Description
TECHNICAL FIELD
[0001] The present invention relates to a strain element and a
physical quantity measurement sensor including the strain element.
In particular, the present invention relates to a strain element, a
method of producing a strain element, and a physical quantity
measurement sensor in each of which the strain element has improved
resistance to fatigue failure and ensures a long-term stable
use.
BACKGROUND ART
[0002] There have conventionally been physical quantity measurement
sensors such as a force sensor, a torque sensor, a load cell, and
the like. A physical quantity measurement sensor detects, through
use of a plurality of strain gauges, strain associated with elastic
deformation caused by an external load (external force), and, from
the results of the detection, measures the values of physical
quantities regarding the external force, moment, and the like. Such
a physical quantity measurement sensor generally includes a metal
strain element that elastically deforms under an external force,
and detects strain by disposing a plurality of strain gauges on
this strain element. Note that specific examples of the physical
quantity measurement sensor are disclosed in Patent Literatures 1
to 5 and Non-patent Literature 1 below.
CITATION LIST
Patent Literature
[0003] [Patent Literature 1] [0004] Japanese Patent Application
Publication Tokukai No. 2016-70673
[0005] [Patent Literature 2] [0006] Japanese Patent Application
Publication Tokukai No. 2011-209178
[0007] [Patent Literature 3] [0008] Japanese Patent Application
Publication Tokukaihei No. 1-262430
[0009] [Patent Literature 4] [0010] Japanese Patent Application
Publication Tokukai No. 2004-45044
[0011] [Patent Literature 5] [0012] Japanese Patent Application
Publication Tokukaihei No. 7-128167
[0013] [Non-Patent Literature 1] [0014] H. Iwasaki, M. Tsumura,
"The principle and application of six-axis Force/Torque sensor",
Automatic Control Joint Lecture Meeting, 49th, held under the
sponsorship of The Institute of Systems, Control and Information
Engineers and others, Nov. 25 and 26, 2006
SUMMARY OF INVENTION
Technical Problem
[0015] A physical quantity measurement sensor is structured such
that, as described earlier, a strain element elastically deforms
under an external force; therefore, if the physical quantity
measurement sensor is used over a long period of time, metal
fatigue builds up in the elastically deformable area of the strain
element. Therefore, there is a problem in that if the built-up
metal fatigue passes a critical point, fatigue failure occurs in
the strain element. Note that the strain element is produced
generally by machining (for example, cutting). Depending on design
specifications and the like, portions having a sharp shape and/or
an acute angled corner shape may be generated. Such portions are
likely to undergo stress concentration when receiving an external
force, and, in such areas where stress concentrates, the risk of
the foregoing fatigue failure is significant.
[0016] Furthermore, a strain gauge disposed on the strain element
is, in some cases, bonded with an adhesive. In a case where the
strain gauge is attached by bonding, depending on the degree of
elastic deformation (e.g., compressive deformation or tensile
deformation) of the strain element, the layer of the adhesive may
not conform to the elastic deformation, and sliding may occur
between the area where the strain gauge is attached and the strain
gauge. If such sliding occurs, a problem arises in that strain
associated with elastic deformation cannot be detected accurately
by the strain gauge and that measurement accuracy decreases.
[0017] Moreover, a strain element employed in a force sensor
disclosed in Patent Literature 1 includes a plurality of arm
portions which connect a central portion with a frame portion. The
strain element is configured such that elastic portions (flexures)
are provided between the frame portion and the arm portions (see
paragraphs 0019 and 0020 of Patent Literature 1), and that each of
the arm portions has a plurality of strain gauges disposed thereon
(see paragraphs 0024, 0025 and FIG. 1 and the like of Patent
Literature 1). The manner in which the strain gauges are disposed,
as shown in FIGS. 1 to 3 and FIGS. 7 to 10, 12 and 13 of Patent
Literature 1, has a problem in that it is difficult to detect
strain associated with deformation when an external force is
exerted on the arm portions in specific directions. Specifically,
there is a problem in accuracy of strain detection when an external
force is exerted in directions Mz, Fx, and Fy shown in FIG. 11 of
Patent Literature 1.
[0018] An aspect of the present invention was made in view of the
above circumstances, and an object thereof is to provide a strain
element, a method of producing a strain element, and a physical
quantity measurement sensor in each of which the strain element has
improved strength (resistance) to fatigue failure.
[0019] Another object of an aspect of the present invention is to
provide a strain element, a method of producing a strain element,
and a physical quantity measurement sensor in each of which, in a
case where a strain gauge is bonded with an adhesive or the like,
the strain gauge is good at conforming to elastic deformation of
the strain element.
[0020] A further object of an aspect of the present invention is to
provide a strain element, a method of producing a strain element,
and a physical quantity measurement sensor in each of which, in a
case where the strain element is configured such that a central
portion and a frame portion are connected by arm portions and that
elastic portions are provided between the frame portion and the arm
portions, the accuracy of strain detection is ensured even if the
arm portions receive an external force in directions such as the
foregoing specific directions.
Solution to Problem
[0021] In order to attain the above object, an aspect of the
present invention is directed to a strain element which is
elastically deformable in response to a load and which is
configured to have a strain gauge disposed thereon, the strain
gauge being configured to detect strain associated with
deformation, the strain element including a strain portion which
corresponds to a region subject to strain and which includes an
area for disposition of the strain gauge, the strain portion being
provided with a residual stress layer having negative residual
stress.
[0022] An aspect of the present invention is directed to a method
of producing a strain element which is elastically deformable in
response to a load and which is configured to have a strain gauge
disposed thereon, the strain gauge being configured to detect
strain associated with deformation, the method including the steps
of: a) masking the strain element except for a strain portion which
corresponds to a region subject to strain and which includes an
area for disposition of the strain gauge; and b) projecting a shot
material at the strain element which has been masked, the step b)
including causing the shot material to collide with the strain
portion and thereby producing the strain element in which the
strain portion is provided with a residual stress layer having
negative residual stress and in which the strain portion has a
surface roughness rougher than a portion other than the strain
portion.
Advantageous Effects of Invention
[0023] According to an aspect of the present invention, a residual
stress layer having compressive residual stress is formed in a
strain portion. It is therefore possible to improve the resistance
to fatigue failure of a portion which elastically deforms and in
which a strain gauge carries out detection. This makes it possible
to achieve a long-term stable use of a physical quantity
measurement sensor in which the strain element in accordance with
an aspect of the present invention is employed.
[0024] According to an aspect of the present invention, a shot
material is projected under the condition in which a strain element
is masked except for the strain portion. Therefore, a residual
stress layer can be formed in the strain portion which is left
unmasked. Furthermore, it is also possible to increase the surface
roughness of the strain portion. This makes it possible to
efficiently produce a strain element which is highly resistant to
fatigue failure and in which a strain gauge of a bonded type is
better at conforming to deformation because of the anchor effect
provided by an adhesive.
BRIEF DESCRIPTION OF DRAWINGS
[0025] FIG. 1 illustrates a force sensor in accordance with
Embodiment 1 of the present invention. (a) of FIG. 1 is a front
view, and (b) of FIG. 1 is a back view.
[0026] FIG. 2 illustrates the force sensor in accordance with
Embodiment 1. (a) of FIG. 2 is a side view, and (b) of FIG. 2 is a
cross-sectional view taken along line A-A in (a) of FIG. 1.
[0027] FIG. 3 is a cross-sectional view of the force sensor
accordance with Embodiment 1, taken along line B-B in (a) of FIG.
1.
[0028] FIG. 4 is a front view of a strain element in accordance
with Embodiment 1 of the present invention.
[0029] FIG. 5 is a back view of the strain element in accordance
with Embodiment 1.
[0030] FIG. 6 is an enlarged view illustrating a manner in which
strain gauges are disposed on one arm portion of the strain element
on the front side.
[0031] FIG. 7 is an enlarged view illustrating a manner in which
strain gauges are disposed on one arm portion of the strain element
on the back side.
[0032] FIG. 8 illustrates the strain element which has been masked.
(a) of FIG. 8 is a front view, (b) of FIG. 8 is a side view, and
(c) of FIG. 8 is a back view.
[0033] FIG. 9 is a circuit diagram for a strain gauge circuit,
illustrating a manner in which strain gauges are electrically
connected.
[0034] FIG. 10 is a block diagram illustrating an internal
configuration of main parts of a signal processing module, which
processes output voltage signals from the strain gauge circuit.
[0035] (a) to (f) of FIG. 11 are tables showing results of
detection by respective bridge circuits included in the strain
gauge circuit.
[0036] FIG. 12 illustrates a strain element in accordance with a
variation of Embodiment 1. (a) of FIG. 12 is a front view, and (b)
of FIG. 12 is a back view.
[0037] FIG. 13 illustrates a strain element in accordance with
another variation of Embodiment 1. (a) of FIG. 13 is a front view,
and (b) of FIG. 13 is a back view.
[0038] FIG. 14 illustrates a variation of masking of the strain
element in accordance with Embodiment 1. (a) of FIG. 14 is a front
view, (b) of FIG. 14 is a side view, and (c) of FIG. 14 is a back
view.
[0039] FIG. 15 illustrates another variation of masking of the
strain element in accordance with Embodiment 1. (a) of FIG. 15 is a
front view, (b) of FIG. 15 is a side view, and (c) of FIG. 15 is a
back view.
[0040] FIG. 16 illustrates a force sensor in accordance with
Embodiment 2 of the present invention. (a) of FIG. 16 is a front
view, (b) of FIG. 16 is a back view.
[0041] FIG. 17 illustrates the force sensor in accordance with
Embodiment 2. (a) of FIG. 17 is a side view, and (b) of FIG. 17 is
a cross-sectional view taken along line C-C in (a) of FIG. 16.
[0042] (a) of FIG. 18 is a cross-sectional view of the force sensor
in accordance with Embodiment 2, taken along line D-D in (a) of
FIG. 16. (b) of FIG. 18 is a cross-sectional view of the force
sensor in accordance with Embodiment 2, taken along line E-E in (a)
of FIG. 16.
[0043] FIG. 19 illustrates a strain element in accordance with
Embodiment 2. (a) of FIG. 19 is a front view, and (b) of FIG. 19 is
a side view.
[0044] FIG. 20 is a back view of the strain element in accordance
with Embodiment 2.
[0045] FIG. 21 illustrates the strain element in accordance with
Embodiment 2 which has been masked. (a) of FIG. 21 is a front view,
(b) of FIG. 21 is a side view, and (c) of FIG. 21 is a back
view.
[0046] FIG. 22 illustrates a variation of masking of the strain
element in accordance with Embodiment 2. (a) of FIG. 22 is a front
view, (b) of FIG. 22 is a side view, and (c) of FIG. 22 is a back
view.
[0047] FIG. 23 illustrates another variation of masking of the
strain element in accordance with Embodiment 2. (a) of FIG. 23 is a
front view, (b) of FIG. 23 is a side view, and (c) of FIG. 23 is a
back view.
[0048] FIG. 24 illustrates a strain element in accordance with
Embodiment 3. (a) of FIG. 24 is a top view (plan view), (b) of FIG.
24 is a front view, and (c) of FIG. 24 is a back view.
[0049] FIG. 25 illustrates the strain element in accordance with
Embodiment 3 which has been masked. (a) of FIG. 25 is a top view
(plan view), (b) of FIG. 25 is a front view, and (c) of FIG. 25 is
a back view.
[0050] FIG. 26 illustrates a strain element in accordance with
Embodiment 4. (a) of FIG. 26 is a top view (plan view), and (b) of
FIG. 26 is a front view.
[0051] FIG. 27 illustrates the strain element in accordance with
Embodiment 4 which has been masked. (a) of FIG. 27 is a top view
(plan view), (b) of FIG. 27 is a front view, and (c) of FIG. 27 is
a back view.
[0052] FIG. 28 illustrates a strain element in accordance with
Embodiment 5. (a) of FIG. 28 is a front view, (b) of FIG. 28 is a
cross-sectional view taken along line F-F in (a) of FIG. 28, and
(c) of FIG. 28 is a cross-sectional view taken along line G-G in
(a) of FIG. 28.
[0053] FIG. 29 illustrates the strain element in accordance with
Embodiment 5 which has been masked. (a) of FIG. 29 is a front view,
(b) of FIG. 29 is a cross-sectional view taken along line F-F in
(a) of FIG. 29, and (c) of FIG. 29 is a cross-sectional view taken
along line G-G in (a) of FIG. 29.
[0054] FIG. 30 illustrates a strain element in accordance with
Embodiment 6. (a) of FIG. 30 is a front view, (b) of FIG. 30 is a
side view, and (c) of FIG. 30 is a plan view.
[0055] FIG. 31 illustrates the strain element in accordance with
Embodiment 6 which has been masked. (a) of FIG. 31 is a front view,
(b) of FIG. 31 is a side view, and (c) of FIG. 31 is a plan
view.
[0056] FIG. 32 illustrates a strain element in accordance with
Embodiment 7. (a) of FIG. 32 is a front view, (b) of FIG. 32 is a
bottom view, and (c) of FIG. 32 is a cross-sectional view taken
along line H-H in (b) of FIG. 32
[0057] FIG. 33 illustrates the strain element in accordance with
Embodiment 7 which has been masked. (a) of FIG. 33 is a front view,
and (b) of FIG. 33 is a bottom view.
DESCRIPTION OF EMBODIMENTS
Embodiment 1
[0058] FIGS. 1 to 3 illustrate a force sensor 1, which is a
specific example of a physical quantity measurement sensor in
accordance with Embodiment 1 of the present invention. (a) of FIG.
1 is a front view of the force sensor 1, (b) of FIG. 1 is a back
view of the force sensor 1, (a) of FIG. 2 is a side view of the
force sensor 1, (b) of FIG. 2 is a cross-sectional view of the
force sensor 1, and FIG. 3 is a cross-sectional view of main parts
of the force sensor 1. The force sensor 1 illustrated in the
drawings such as FIG. 1 is for application in an industrial robot
arm. As illustrated in (a) of FIG. 2, the force sensor 1 has a
structure in which three disk-shaped members are stacked together.
Furthermore, as illustrated in (a) of FIG. 2, the force sensor 1 is
configured such that a table block 2 is attached to a robot
hand-side (front side) and a base block 6 is attached to a robot
arm-side (back side), and such that the strain element 10 in
accordance with Embodiment 1 of the present invention is sandwiched
between the table block 2 and the base block 6.
[0059] The following description discusses X axis, Y axis, and Z
axis shown in the drawings such as FIGS. 1 and 2. The X axis is an
axis that is parallel to the horizontal direction (transverse
direction) of the force sensor 1. The Y axis, which is orthogonal
to the X axis, is an axis that is parallel to the vertical
direction (height direction) of the force sensor 1. The Z axis,
which is orthogonal to the X axis and the Y axis, is an axis that
is parallel to the thickness direction of the force sensor 1 (the
same applies to the following descriptions). The force sensor 1 in
accordance with Embodiment 1 is capable of measuring values
regarding external force in directions of the respective X, Y and Z
axes and moments about the respective X, Y and Z axes through
strain detection by a plurality of strain gauges provided on the
strain element 10 (force sensor 1 corresponds to a six-axis force
sensor).
[0060] As illustrated in (a) of FIG. 1, the table block 2 is in the
shape of a circle when viewed from front side, and has many holes
(through-holes) in a flat front face 2a corresponding to the front
side. Specifically, the table block 2 has, in the vicinity of the
center of a circle, bolt through-holes 3a, 3b, and 3c (countersunk
through-holes for passage of bolts) which are arranged to form an
equilateral triangle symmetrical with respect to center line Y1 in
the height direction. The table block 2 also has locating
through-holes 4a, 4b, and 4c (through-holes with fit tolerance)
which are arranged to form an inverted equilateral triangle
symmetrical with respect to the center line Y1. The table block 2
further has hand-attaching screw holes 5a, 5b, and 5c (internally
threaded holes) which are arranged in the vicinity of the outer
circumference to form an inverted equilateral triangle. These
hand-attaching screw holes 5a, 5b, and 5c are used for attachment
to the robot hand.
[0061] Furthermore, the table block 2 has, on a back face 2b
opposite the foregoing front face 2a, a doughnut-shaped groove 2c
around a center portion 2d which has the foregoing bolt
through-holes 3a to 3c and locating through-holes 4a to 4c (see
FIG. 1 and (b) of FIG. 2). The thickness (dimension along the Z
axis direction) of the outer contour of the groove 2c is slightly
less than the thickness of the center portion 2d, and thereby a
shape in which the center portion 2d slightly protrudes is
provided. With this, the back face 2b of the center portion 2d of
the table block 2 makes contact with a front face 10a of the strain
element 10, when the force sensor 1 is in an assembled state.
[0062] On the other hand, the base block 6 is also in the shape of
a circle when seen from back side, as illustrated in (b) of FIG. 1.
The base block 6 has arm-attaching screw holes 7a, 7b, and 7c
(internally threaded holes) which are arranged in the vicinity of
the outer circumference of a flat front face 6a corresponding to
the back side to form an inverted equilateral triangle. The
arm-attaching screw holes 7a, 7b, and 7c in the base block 6 are
used for attachment to the robot arm. Furthermore, the back face
6b, opposite the front face 6a, has a hollow 6c in the center
portion as also illustrated in (b) of FIG. 2. The back face 6b is
provided with screw holes 8a, 8b, and 8c (internally threaded
holes) which are arranged in the vicinity of the outer
circumference to form an equilateral triangle. The back face 6b
also has locating holes 9a to 9c such that the locating holes 9a to
9c are adjacent to the respective screw holes 8a to 8c (see holes
represented by dashed lines in (b) of FIG. 1). Note that such table
block 2 and base block 6 are each produced from a lightweight metal
material (for example, aluminum-based material) in order not to
greatly affect the weight capacity of an industrial robot arm to
which the force sensor 1 is applied.
[0063] FIGS. 4 and 5 illustrate a front side and a back side of the
strain element 10 in accordance with Embodiment 1 of the present
invention. As illustrated in (a) of FIG. 2, the strain element 10
is a plate-like member which is smaller in dimension in the
thickness direction (dimension in the Z axis direction) than the
foregoing table block 2 and base block 6, and has a circular
circumferential outline when seen from the front side and the back
side. The strain element 10 includes: a peripheral frame portion
11; a central portion 12 which is located in a space defined by the
frame portion 11 so as to be spaced apart from the frame portion
11; and three arm portions 20, 21 and 22 which connect the frame
portion 11 and the central portion 12. Note that, in this example,
the arm portions 20 to 22 are included in strain portions which
correspond to regions subject to strain associated with elastic
deformation.
[0064] The arm portions 20 to 22 radially extend outward from the
center of the strain element 10, and are disposed along a
circumferential direction of the strain element 10 having a
circular outer circumference so as to be spaced apart from each
other by 120 degrees. Each of such arm portions 20 to 22 is,
because of the structure, less rigid than the frame portion 11 and
the central portion 12, and each of the arm portions 20 to 22 is
configured to elastically deform in response to an external load or
moment.
[0065] The central portion 12 has an outer circumference
substantially in the shape of an equilateral hexagon, and has,
within the outer circumference, screw through-holes 13a, 13b, and
13c (internally threaded through-holes) which are arranged to form
an equilateral triangle, and locating through-holes 14a, 14b, and
14c (through-holes with fit tolerance) which are arranged to form
an inverted triangle. The screw through-holes 13a to 13c correspond
to the bolt through-holes 3a to 3c of the foregoing table block 2,
and the locating through-holes 14a to 14c correspond to the
locating through-holes 4a to 4c of the foregoing table block 2.
Furthermore, the central portion 12, whose outline is substantially
in the shape of a hexagon, connects to the arm portions 20,21, and
22 at middle portions of outer peripheral edge portions 12c, 12d,
and 12e which are adjacent to and correspond to the locating
through-holes 14a, 14b, and 14c.
[0066] The frame portion 11 has an outer contour in the form of a
circle, and an inner contour in the form of a hexagon which is
obtained by uniformly enlarging the contour of the foregoing
central portion 12. The frame portion 11 has bolt through-holes
18a, 18b, and 18c which are arranged to from an equilateral
triangle, and locating through-holes 19a to 19c which are arranged
adjacent to the respective bolt through-holes 18a to 18c. The bolt
through-holes 18a to 18c correspond to the screw holes 8a to 8c of
the foregoing base block 6, and the locating through-holes 19a to
19c correspond to the locating holes 9a to 9c of the foregoing base
block 6.
[0067] The frame portion 11 is connected to the arm portions 20,
21, and 22 at middle portions of inner peripheral edge portions
11c, 11d, and 11e located opposite the outer peripheral edge
portions 12c, 12d, and 12e of the foregoing central portion 12.
Because of the presence of such arm portions 20, 21, and 22, the
space between the frame portion 11 and the central portion 12 is
divided into three, resulting in formation of a first space 15, a
second space 16, and a third space 17. The frame portion 11 further
has three through-openings 25, 26, and 27 (each corresponding to
first through-opening) in the junctions where the frame portion 11
connects to the respective arm portions 20 to 22. These
through-openings 25 to 27 are in the shape of straight lines along
the inner peripheral edge portions 11c, 11d, and 11e at the inner
circumference in the form of a hexagon, and are equal to or
slightly greater in length than the edges of the respective inner
peripheral edge portions 11c, 11d, and 11e. Each of the
through-openings 25 to 27 has a width that is set to a value within
the range of about 1/8 to 1/5 of its length (in Embodiment 1, set
to about 1/6.5).
[0068] The strain element 10 has the through-openings 25 to 27 in
the frame portion 11, and is thereby arranged so that deformability
in directions of stretch of the arm portions 20 to 22 is reduced
and that strain of the arm portions 20 to 22 associated with
elastic deformation, in directions other than the directions of
stretch, is easily detected.
[0069] The arm portions 20 to 22, which are elastically deformable,
each have, disposed on its arm front face 20a, 21a or 22a
illustrated in FIG. 4 corresponding to the front side of the strain
element 10, a set of four strain gauges (strain gauges C1 to C4,
strain gauges B1 to B4, or strain gauges A1 to A4). Also, the arm
portions 20 to 22 each have, disposed on its arm back face 20b,
21b, or 22b illustrated in FIG. 5 corresponding to the back side of
the strain element 10, a set of four strain gauges C1' to C4',
strain gauges B1' to B4', or strain gauges A1' to A4'.
[0070] Such strain gauges A1 to C4' carry out detection of strain
associated with elastic deformation of the arm portions 20 to 22.
The strain is detected from an electric change in resistance that
occurs when the arm portions 20 to deform. The strain gauges A1 to
C4' change their resistance in response to deformation of the arm
portions. Therefore, strain is detected based on a change in output
voltage of a bridge circuit illustrated in FIG. 9 (described later)
associated with a change in resistance in the bridge circuit.
Furthermore, the strain gauges A1 to C4' are capable of detecting
strain in respective predetermined directions (hereinafter
"detection directions"). By arranging the strain gauges A1 to C4'
so that their detection directions are oriented as desired,
detection suitable for strain such as bending, shearing, and/or the
like of the arm portions 20 to 22 is carried out (see explanations
for FIGS. 6 and 7 provided later).
[0071] The strain gauges A1 to C4' are each composed of: a thin
metal film containing Cu--Ni as a main material and including a
pattern; and a flexible resin film (polyimide-and-epoxy-based
resin) that covers the thin metal film. Note that the main material
for the strain gauges A1 to C4' is not limited to the above
mentioned main material. Besides the above-mentioned main material,
also Cu, Ni, Al, Ti, Cr, Ge, Ni--Cr, Si semiconductor, Cr--O,
Cr--N, and the like can be used as the main material. Furthermore,
the strain gauges A1 to C4' used in Embodiment 1 are of a type in
which a base material for a strain gauge is coated with a strain
gauge main material.
[0072] FIG. 6 illustrates, with use the arm portion 21 parallel to
the Y axis direction as an example, a manner in which strain gauges
are disposed on an arm front face corresponding to the front side
of the strain element 10. The arm portion 21 has the strain gauges
B1 to B4 disposed on the arm front face 21a (corresponding to one
face of the arm portion). On the arm portion 21, the strain gauges
B1 to B4 are disposed such that they are symmetrical with respect
to center line Y10 which extends along the direction of extension
of the arm portion 21 (corresponding to a direction which connects
the central portion 12 with the frame portion 11) (line that is
parallel to the Y axis on the arm front face 21a and that passes
through the center of the strain element 10).
[0073] Specifically, the strain gauges B1 and B2 (corresponding to
the first strain gauge and the second strain gauge), of the set of
four strain gauges B1 to B4, are disposed in an area close to the
central portion 12 such that their detection directions K1 and K2
are parallel to the center line Y10. Note that, in FIG. 6,
square-shaped parts disposed vertically on the left-hand side of
the strain gauge B1 are connection parts B1a and B1b (positive and
negative connection parts) for electrical connection to the strain
gauge B1. These connection parts B1a and B1b have a lead wire (not
illustrated) connected thereto (the same applies to square-shaped
parts adjacent to the other strain gauges B2 to B4 illustrated in
FIG. 6).
[0074] The strain gauges B3 and B4 (corresponding to the third
strain gauge and the fourth strain gauge), of the set of four
strain gauges B1 to B4, are disposed in an area close to the frame
portion 11 such that their detection directions K3 and K4 are at an
angle to the center line Y10 so as to diverge away from each other
with decreasing distance to the central portion 12. Note that, in
Embodiment 1, the detection directions K3 and K4 are each at an
angle of 45 degrees to the center line Y10. The manner of
disposition has been discussed using the strain gauges B1 to B4 on
the arm front face 21a of the arm portion 21 as an example.
However, the same applies to the disposition of the strain gauges
C1 to C4 on the arm front face 20a of the arm portion 20 and to the
disposition of the strain gauges A1 to A4 on the arm front face 22a
of the arm portion 22.
[0075] FIG. 7 illustrates, with use of the arm portion 21 parallel
to the Y axis direction as an example, a manner in which strain
gauges are disposed on an arm back face corresponding to the back
side of the strain element 10, similarly to the case of FIG. 6. The
disposition illustrated in FIG. 7 is one obtained by flipping the
disposition illustrated in FIG. 6 about center line Y11 (center
line of the arm back face, corresponding to the center line Y10
illustrated in FIG. 6).
[0076] Specifically, the strain gauges B1' and B3', of the four
strain gauges B1' to B4', are positioned on the right-hand side of
the center line Y11, and the strain gauges B2' and B4' of the four
strain gauges B1' to B4' are positioned on the left-hand side of
the center line Y11, such that the strain gauges B1' and B3' and
the strain gauges B2' and B4' are symmetrical with respect to the
center line Y11. Furthermore, the strain gauges B1' and B2'
(corresponding to the first strain gauge and the second strain
gauge) are disposed in an area close to the central portion 12 such
that their respective detection directions K1' and K2' are parallel
to the center line Y11. The strain gauges B3' and B4'
(corresponding to the third strain gauge and the fourth strain
gauge) are disposed in an area close to the frame portion 11 such
that their detection directions K3' and K4' are at an angle to the
center line Y11 so as to diverge away from each other with
decreasing distance to the central portion 12. Note that the angle
here is the same as that of FIG. 6, and is 45 degrees.
[0077] Note that square-shaped parts illustrated adjacent to each
strain gauge, such as the strain gauge B1', illustrated in FIG. 7
are electrical connection parts, as with the case of FIG. 6. The
manner of disposition has been discussed using the strain gauges
B1' to B4' on the arm back face 21b of the arm portion 21 as an
example. However, the same applies to the disposition of the strain
gauges C1' to C4' on the arm back face 20b of the arm portion 20
and to the disposition of the strain gauges A1' to A4' on the arm
back face 22b of the arm portion 22.
[0078] (a) to (c) of FIG. 8 illustrate a masked state in a surface
processing step of a process of producing the strain element 10 on
which the strain gauges A1 to C4' are to be disposed (such a
process corresponds to a method of producing a strain element in
accordance with Embodiment 1 of the present invention). The strain
element 10 itself is made mainly from a lightweight, elastically
deformable metal material. For example, by cutting an
aluminum-based material (such as A5052) or a stainless-steel-based
material (such as SUS304) by machining, it is possible to form the
material into the shape illustrated in the foregoing drawings such
as FIGS. 4 and 5.
[0079] However, machining (cutting) alone is insufficient to avoid,
for example, generation of burrs on peripheries of a processed
product (unfinished strain element 10), and portions shaped like
corners (corner portions) are likely to undergo stress
concentration when a load (external force) is exerted. To address
this, the step of corner easing is carried out with respect to a
machined, processed product, and thereby burrs and the like are
removed from edges, corners, and the like, at each of which two or
more faces meet, of the peripheries of the processed product. Note
that such corner easing may be carried out by any of slight
chamfering, chamfering, or filleting; however, it is preferable
that the corners of the portions that are likely to undergo stress
concentration are eased by filleting to eliminate sharp corners and
thereby the occurrence of stress concentration is prevented as much
as possible.
[0080] In Embodiment 1, areas enclosed by dot-dot-dash lines
illustrated in FIGS. 6 and 7 are filleted. Specifically, the strain
element 10, which has a shape illustrated in the drawings such as
FIGS. 4 and 5, is structured such that the frame portion 11 and the
central portion 12 are connected by the arm portions 20 to 22.
Corner portions (for example, corner portions corresponding to the
areas enclosed by dot-dot-dash lines with signs 21g and 21h in
FIGS. 6 and 7) at edges of a junction where the frame portion 11
and the arm portion 20, 21, or 22 connect to each other (the
junction is, for example, the area indicated by sign 21d in FIGS. 6
and 7) are portions where stress concentration is likely to occur.
Also, corner portions (for example, corner portions corresponding
to the areas enclosed by dot-dot-dash lines with signs 21e and 21f
in FIGS. 6 and 7) of edges of a junction where the central portion
12 and the arm portion 20, 21, or 22 connect to each other (the
junction is, for example, the area indicated by sign 21c in FIGS. 6
and 7) are portions where stress concentration is likely to occur.
Therefore, these corner portions corresponding to the areas with
the signs 21e, 21f, 21g, and 21h, enclosed by dot-dot-dash lines,
are filleted and stress concentration is to be reduced. Note that
the radius of filleting can be a value within the range of about
0.1 to 0.3 mm, and, because of, for example, the relationship in
dimensions between the strain element 10 and the arm portions 20 to
22, a value around 0.2 mm is preferred. Note that the radius of
curvature (for example, the radius of curvature R corresponding to
the sign 21e in FIGS. 6 and 7) of each of the corner portions
indicated by the signs 21e to 21h illustrated in FIGS. 6 and 7 can
have a value within the range of about 1.5 to 3.5 mm, and, in one
example, a value of about 2 mm can be employed.
[0081] After the foregoing machining and corner easing are carried
out, surface processing is carried out. Before the surface
processing step is carried out, the strain element 10 is masked as
illustrated in (a) to (c) of FIG. 8. Note that the cross-hatched
areas in (a) to (c) of FIG. 8 correspond to masked areas. Also in
the following descriptions, the cross-hatched areas correspond to
masked areas.
[0082] In this masking step, the strain element 10 is masked by
adhesive tape T except for the arm portions 20 to 22 which include
areas for disposition of the strain gauges A1 to C4' (i.e., the
frame portion 11 and the central portion 12 are masked). Note that
side faces in the thickness direction, such as outwardly facing
faces of the central portion 12, inwardly facing faces of the frame
portion 11, and an outwardly facing face 10c of the strain element
10 (frame portion 11), are also masked. Therefore, with regard to
each of the arm portions 20 to 22 which are left unmasked, an area
extending from a corresponding one of central junctions 20c to 22c
(where the arm portion connects to the central portion 12) to a
corresponding one of outer junctions 20d to 22d (where the arm
portion connects to the frame portion 11) of a corresponding one of
the arm front faces 20a to 22a is exposed. Also, on each of the arm
back faces 20b to 22b, an area extending from a corresponding one
of the central junctions 20c to 22c to a corresponding one of the
outer junctions 20d to 22d (where the arm portion connects to the
frame portion 11) is exposed. Furthermore, opposite side faces of
each of the arm portions 20 to 22 are also exposed. As such, all
four sides of each of the arm portions 20 to 22 are exposed.
[0083] Next, the strain element 10 which has been masked is
inserted into a shot blasting machine (or shot peening machine),
and the step of projecting a shot material at the strain element 10
and thereby causing the shot material to collide with the strain
element 10 is carried out. Examples of the shot material include
abrasive grains, steel shots, steel grids, cut wires, glass beads,
and organic matter. In this step, the four sides of each of the arm
portions 20 to 22, which are left unmasked, are only struck
directly with the shot material. Therefore, the four sides
(surfaces) of each of the arm portions 20 to 22 undergo plastic
deformation due to collision with the shot material, and a residual
stress layer having compressive residual stress (negative residual
stress) (compressive residual stress layer which will become a
hardened surface layer) is formed. Also, the four sides (surfaces)
of each of the arm portions 20 to 22 are given a surface roughness
rougher than those of the masked areas.
[0084] In the above step, the shot material collides also with the
masked areas; however, the force of the collision is weakened by
the mask. Thus, the collision is indirect collision, and the
residual stress occurring in the non-masked arm portions 20 to 22
is greater (in absolute value of the compressive residual stress)
than those in the other masked portions. The main material for use
in masking is preferably one that enables easy masking operation,
like a tape material such as adhesive tape. However, any material
that can cover the strain element and thereby alleviate the
colliding force of the shot material can be employed (besides tape,
various kinds of coating materials can be employed).
[0085] Note that the following description will discuss an example
in which the projection was carried out (shot blasting was carried
out) with respect to a stainless-steel-based member (SUS304) as the
strain element 10 with use of abrasive grains as the shot material.
On each of the arm portions 20 to 22, a residual stress layer
having a -938 MPa residual stress (negative residual stress) is
formed. Also, the surface roughness, whose value before processing
was Rz (maximum roughness depth)=1.020 .mu.m, became Rz=7.682 .mu.m
after the processing. The surface roughness after the processing
was about 7 times as much as that before the processing.
[0086] With regard to the strain element 10 which has undergone
such surface processing, on each of the non-masked arm portions 20
to 22, a residual stress layer having a negative residual stress
greater in absolute value than those in the other masked portions
was formed. With this, the arm portions 20 to 22 increase in
fatigue strength against elastic deformation, fatigue life is
prolonged, and this makes it possible to achieve a long-term stable
use of the force sensor 1 (physical quantity measurement
sensor).
[0087] Furthermore, the surface roughness of the arm portions 20 to
22 is rougher than those of portions other than the arm portions 20
to 22. Therefore, in a case where the strain gauges A1 to C4' are
attached (bonded) with an adhesive to the arm front faces 20a to
22a and the arm back faces 20b to 22b of the arm portions 20 to 22
in the foregoing manners after the step of projecting the shot
material, because of the roughness of the arm front faces 20a to
22a and the arm back faces 20b to 22b, the bonded strain gauges A1
to C4' are well anchored, and adhesiveness becomes greater than
conventional techniques. With this, the strain gauges A1 to C4' are
more likely to conform to elastic deformation of the arm portions
20 to 22, and the accuracy of detection by the strain gauges A1 to
C4' improves.
[0088] Next, the following description will discuss how the
foregoing table block 2, base block 6, and strain element 10 are
assembled to form the force sensor 1 (see the drawings such as
FIGS. 1 to 4). First, the strain element 10 and the base block 6
are stacked together such that a back face 10b of the strain
element 10 (back face 11b of the frame portion 11) faces and makes
contact with the back face 6b of the base block 6.
[0089] Before doing so, locating pins P are press-fit into the
locating holes 9a to 9c of the base block 6. The strain element 10
and the base block 6 are positioned so that the locating pins P in
the respective locating holes 9a to 9c are press-fit into the
locating through-holes 19a to 19c in the frame portion 11 of the
strain element 10 when the strain element 10 is placed on the base
block 6, and then the strain element 10 and the base block 6 are
stacked together (see FIG. 3). When the strain element 10 and the
base block 6 are stacked together after they are positioned like
above, the bolt through-holes 18a to 18c in the frame portion 11 of
the strain element 10 are brought into a condition in which they
are in communication with the screw holes 8a to 8c of the base
block 6. Therefore, bolts N (hexagon socket head bolts) are put
through the bolt through-holes 18a to 18c of the strain element 10
and fastened to the screw holes 8a to 8c of the base block 6, and
the strain element 10 is fixed to the base block 6 such that the
strain element 10 is placed on the base block 6 (see (b) of FIG.
2).
[0090] Next, the strain element 10 and the table block 2 are
stacked together such that a front face 10a of the strain element
10 (front face 12a of the central portion 12) faces and makes
contact with the back face 2b of the table block 2. Before doing
so, locating pins P are press-fit into the locating through-holes
14a to 14c in the central portion 12 of the strain element 10. When
the table block 2 is placed on the strain element 10, the table
block 2 is placed on the strain element 10 such that the locating
pins P in the respective locating through-holes 14a to 14c are
press-fit into the locating through-holes 4a to 4c in the table
block 2.
[0091] When the table block 2 and the strain element 10 are stacked
together such that they are positioned like above, the bolt
through-holes 3a to 3c in the table block 2 are brought into a
condition in which they are in communication with the screw
through-holes 13a to 13c of the strain element 10. Therefore, bolts
N (hexagon socket head bolts) are put through the bolt
through-holes 3a to 3c of the table block 2 and fastened to the
screw through-holes 13a to 13c of the strain element. The table
block 2 is fixed to and attached to the strain element 10 in a
state in which the table block 2 is placed on the strain element
10, thereby completing the force sensor 1.
[0092] The general shape of the finished force sensor 1 is in the
form of a cylinder as shown in (a) of FIG. 2. On the other hand,
the table block 2 is shaped such that, as described earlier, the
center portion 2d of the back face 2b protrudes more than the
peripheral portion of the back face 2b. Because of this, there is
clearance S between the peripheral portion of the table block 2 and
the front face 10a of the strain element 10 (front face 11a of the
frame portion 11).
[0093] Then, with regard to the finished force sensor 1, the front
face 6a of the base block 6 is attached to an end face at an end
portion of an industrial robot arm, and the front face 2a of the
table block 2 is attached to a back end face of a robot hand. Then,
when the industrial robot arm operates and the robot hand grabs an
object such as a workpiece, a load (external force) caused by an
impact resulting from the grabbing or the like is transmitted from
the robot hand to the table block 2. The load having been
transmitted to the table block 2 is transmitted to the central
portion 12, of the strain element 10, which is in contact with the
center portion 2d of the table block 2.
[0094] The central portion 12 of the strain element 10 is a rigid
body having a predetermined rigidity, whereas the frame portion 11
of the strain element 10 is also fixed to the base block 6.
Therefore, the load having been transmitted to the central portion
12 as described above is exerted on the arm portions 20 to 22,
which are lower in rigidity than the central portion 12 and the
frame portion 11. With this, the arm portions 20 to 22 elastically
deform. The manner in which the arm portions 20 to 22 elastically
deform depends on the area of the central portion 12 of the strain
element 10 to which the load is transmitted. For example, when the
central portion 12 receives a depressing load at or near the
junction where the central portion 12 connects to the arm portion
20, the arm portion 20 elastically deforms in a manner such that
its portion connected to the central portion 12 flexes toward the
base block 6. On the contrary, the other arm portions 21 and 22
elastically deform in a manner such that their portion connected to
the central portion 12 flexes toward the table block 2.
[0095] According to the strain element 10 in accordance with
Embodiment 1 of the present invention, even if the arm portions 20
to 22 elastically deform repeatedly, each of the arm portions 20 to
22 has a residual stress layer formed on its four sides as
described earlier. Therefore, the strain element 10 is less likely
to undergo fatigue failure over a long period of time. Furthermore,
as described earlier, in the strain element 10, the strain gauges
A1 to C4' disposed on the arm portions 20 to 22 are good at
conforming to elastic deformation of the arm portions 20 to 22.
[0096] The degree of flexion of the arm portions 20 to 22, which
are elastically deformable under a load, is detected by the strain
gauges A1 to C4' disposed on the arm portions 20 to 22. With this,
at the force sensor 1, forces and moments in respective directions
(six-axis forces) exerted on the central portion 12 of the strain
element 10 are measured. The six-axis forces measured include:
force Fx in the X axis direction; force Fy in the Y axis direction;
force Fz in the Z axis direction; moment Mx about the X axis
direction; moment My about the Y axis direction; and moment Mz
about the Z axis direction, which are exerted on the central
portion 12. Next, an electrical system for measurement of these
six-axis forces is discussed.
[0097] FIG. 9 is a circuit diagram for a strain gauge circuit 29,
illustrating a manner in which the twenty-four strain gauges A1 to
C4' disposed on the strain element 10 as described earlier are
electrically connected. The strain gauge circuit 29, in which the
twenty-four strain gauges A1 to C4' are connected, includes six
bridge circuits I to VI. Each of the first to third bridge circuits
I to III is a bridge circuit constituted by strain gauges, which
are disposed in areas close to the central portion 12, of the
strain gauges disposed on the arm portions 20 to 22. Each of the
fourth to sixth bridge circuits IV to VI is a bridge circuit
constituted by strain gauges, which are disposed in areas close to
the frame portion 11, of the strain gauges disposed on the arm
portions 20 to 22.
[0098] Specifically, the first bridge circuit I is a bridge circuit
in which the strain gauges A1 and A2 (which are disposed in the
area close to the central portion 12 on the arm front face 22a of
the arm portion 22) and the strain gauges A1' and A2' (which are
disposed in the area close to the central portion 12 on the arm
back face 22b of the arm portion 22) are connected together. In the
first bridge circuit I illustrated in FIG. 9, the manner of
connection is such that the strain gauges A1 and A2 are opposite
each other and the strain gauges A1' and A2' are opposite each
other (the second bridge circuit II and the third bridge circuit
III also employ similar manners of connection.)
[0099] The second bridge circuit II is a bridge circuit in which
the strain gauges B1 and B2 (which are disposed in the area close
to the central portion 12 on the arm front face 21a of the arm
portion 21) and the strain gauges B1' and B2' (which are disposed
in the area close to the central portion 12 on the arm back face
21b of the arm portion 21) are connected together. The third bridge
circuit III is a bridge circuit in which the strain gauges C1 and
C2 (which are disposed in the area close to the central portion 12
on the arm front face 20a of the arm portion 20) and the strain
gauges C1' and C2' (which are disposed in the area close to the
central portion 12 on the arm back face 20b of the arm portion 20)
are connected together.
[0100] Furthermore, the fourth bridge circuit IV is a bridge
circuit in which the strain gauges A3 and A4 (which are disposed in
the area close to the frame portion 11 on the arm front face 22a of
the arm portion 22) and the strain gauges A3' and A4' (which are
disposed in the area close to the frame portion 11 on the arm back
face 22b of the arm portion 22) are connected together. In the
fourth bridge circuit I illustrated in FIG. 9, the manner of
connection is such that the strain gauges A3 and A3' are opposite
each other and the strain gauges A4 and A4' are opposite each other
(the second bridge circuit II and the third bridge circuit III also
employ similar manners of connection.)
[0101] The fifth bridge circuit V is a bridge circuit in which the
strain gauges B3 and B4 (which are disposed in the area close to
the frame portion 11 on the arm front face 21a of the arm portion
21) and the strain gauges B3' and B4' (which are disposed in the
area close to the frame portion 11 on the arm back face 21b of the
arm portion 21) are connected together. The sixth bridge circuit VI
is a bridge circuit in which the strain gauges C3 and C4 (which are
disposed in the area close to the frame portion 11 on the arm front
face 20a of the arm portion 20) and the strain gauges C3' and C4'
(which are disposed in the area close to the frame portion 11 on
the arm back face 20b of the arm portion 20) are connected
together.
[0102] The above-described strain gauge circuit 29 is arranged such
that an input power supply voltage Ein is applied to each of the
bridge circuits I to VI. Then, during the application of this
voltage, the first bridge circuit I outputs an output voltage
signal CH-I through its output terminal. Similarly, the second
bridge circuit II outputs an output voltage signal CH-II, the third
bridge circuit III outputs an output voltage signal CH-III, the
fourth bridge circuit IV outputs an output voltage signal CH-IV,
the fifth bridge circuit V outputs an output voltage signal CH-V,
and the sixth bridge circuit VI outputs an output voltage signal
CH-VI.
[0103] FIG. 10 is a block diagram illustrating an internal
configuration of main parts of a signal processing module 30, which
processes the output voltage signals CH--I to CH-VI outputted from
the foregoing strain gauge circuit 29 illustrated in FIG. 9. The
signal processing module 30 includes an amplifier 31, an A-D
converter 32, a processor 33, a memory 34, and a D-A converter 35.
The amplifier 31 is electrically connected to the output terminal
of the strain gauge circuit 29 illustrated in FIG. 9, and contains
AMP-I to AMP-VI for individually amplifying the output voltage
signals CH--I to CH-VI from the strain gauge circuit 29,
respectively.
[0104] Amplified signals (analog signals) amplified by the AMP-I to
AMP-VI of the amplifier 31, respectively, are converted into
digital signals through the A-D converter 32, and then inputted to
the processor 33. The processor 33 serves to carry out a process of
calculating the foregoing six-axis forces (Fx, Fy, Fz, Mx, My, and
Mz) exerted on the central portion 12 of the strain element 10. The
forces are the results of measurement by the force sensor 1. The
processor 33 carries out the calculation process based on the
following equation (1) while referring to a calibration matrix C
stored in the memory 34.
F=C.times.E (1)
[0105] In the equation (1) above, F is a matrix of equation (2)
below, which represents the foregoing six-axis forces (Fx, Fy, Fz,
Mx, My, and Mz) exerted on the central portion 12. C is a
calibration matrix of equation (3) below. E is a matrix of values
obtained by converting the output voltage signals CH--I to CH-VI of
the strain gauge circuit 29 from analog to digital (see equation
(4) below).
F = ( Fx Fy Fz M .times. .times. x My Mz ) ( 2 ) C = ( C 11 C 12 C
13 C 14 C 15 C 16 C 21 C 22 C 23 C 24 C 25 C 26 C 31 C 32 C 33 C 34
C 35 C 36 C 41 C 42 C 43 C 44 C 45 C 46 C 51 C 52 C 53 C 54 C 55 C
56 C 61 C 62 C 63 C 64 C 65 C 66 ) ( 3 ) E = ( E 11 E 21 E 31 E 41
E 51 E 61 ) ( 4 ) ##EQU00001##
[0106] Note that, in the calibration matrix C represented by the
above equation (3), values (pre-calculated values) specific to each
force sensor are used. Specifically, specific values of the
elements of the calibration matrix C are found from (i) conditions
in which the six-axis forces (Fx, Fy, Fz, Mx, My, and Mz) are
exerted on the force sensor and (ii) the results of detection by
the strain gauges A1 to C4' associated with elastic deformation of
the arm portions 20 to 22 in those conditions.
[0107] As shown in the foregoing equation (1), the processor 33
multiplies the calibration matrix C of the equation (3) by the
matrix E of the A-D converted values which are based on the output
voltage signals from the A-D converter 32, and thereby finds F
which is a matrix of the six-axis forces (Fx, Fy, Fz, Mx, My, and
Mz). The processor 33 makes it possible to output the result of the
calculation (corresponding to physical quantity corresponding to
elastic deformation of the strain element 10 under a load) as a
digital signal. The processor 33 also makes it possible to output
the result of the calculation by analog signal through the D-A
converter 35. Such an output value (output value by digital or
analog signal) serves as a physical quantity measured by the force
sensor 1.
[0108] Note that the signal processing module 30 illustrated in
FIG. 10 is disposed in the hollow 6c of the base block 6 of the
force sensor 1 (see (b) of FIG. 2). Also, the signal processing
module 30 is arranged such that lead wires for transmission of the
output signal from the processor 33 and the output signal from the
D-A converter 35 extend outward through a cutout 6e in a peripheral
wall 6d of the base block 6 (see (a) of FIG. 2).
[0109] (a) to (f) of FIG. 11 are tables for the respective bridge
circuits I to VI, in each of which, with regard to the foregoing
force sensor 1, cases where an external force and/or a moment (Fx,
Fy, Fz, Mx, My, and/or Mz) is/are applied to the table block 2 with
the base block 6 fixed are compared with no-load conditions. The
tables show how the resistances of the strain gauges A1 to C4'
change and whether or not voltage values of the output voltage
signals CH--I to CH-V from the bridge circuits I to VI have
changed, that is, whether or not there is unbalanced output.
[0110] In the force sensor 1, in a case where the external force Fy
in the Y axis direction is exerted on the central portion 12 while
the frame portion 11 is fixed, forces act on the arm portions 20
and 22 and the arm portions 20 and 22 become deformed; however,
strain does not occur in the arm portion 21 because the junction
where the arm portion 21 connects to the frame portion 11, near the
through-opening 26, flexes. In a case where the external force Fx
in the X axis direction is exerted on the central portion 12 while
the frame portion 11 is fixed, forces act on the arm portions 20 to
22, respectively, and strain occurs. In a case where the external
force Fz in the Z axis direction is exerted on the central portion
12 while the frame portion 11 is fixed, the arm portions 20 to 22
flex in a uniform manner.
[0111] Furthermore, in the force sensor 1, in a case where the
moment My about the Y axis direction is exerted on the central
portion 12 while the frame portion 11 is fixed, the arm portion 21
is merely twisted and does not flex, whereas moments act on the arm
portions 20 and 22 and the arm portions 20 and 22 flex. In a case
where the moment Mx about the X axis direction is exerted on the
central portion 12 while the frame portion 11 is fixed, moments act
on the arm portions 20 to 22, respectively, and the arm portions 20
to 22 flex. In a case where the moment Mz about the Z axis
direction is exerted on the central portion 12 while the frame
portion 11 is fixed, the arm portions 20 to 22 flex in a uniform
manner.
[0112] As has been described, according to the force sensor 1 in
accordance with Embodiment 1, a compressive residual stress layer
(layer having negative residual stress) is formed on surfaces (four
sides) of each of the arm portions 20 to 22 of the strain element
10, and therefore the force sensor 1 has improved metal fatigue
strength associated with elastic deformation. Furthermore, since
stress concentration is reduced in corner portions at edges of
junctions where the respective arm portions 20 to 22 connect to the
frame portion 11 and in corner portions at edges of junctions where
the respective arm portions 20 to 22 connect to the central portion
12, working life of the force sensor 1 as a whole as a sensor is
longer than conventional sensors. Furthermore, in the force sensor
1 in accordance with Embodiment 1, the strain gauges A1 to C4'
disposed on the arm portions 20 to 22 are good at conforming to the
arm portions 20 to 22 when the arm portions 20 to 22 elastically
deform. Therefore, when the arm portions 20 to 22 elastically
deform, sliding is less likely to occur between the strain gauges
A1 to C4' and the arm portions 20 to 22, and thereby measurement
accuracy is improved as compared to conventional sensors. In
addition, since the strain gauges A1 to C4' are disposed in a
special manner (see the disposition of the strain gauges B3, B4,
B3' and B4' and the like in FIGS. 6 and 7), the accuracy of
detection and measurement concerning strain when the moment and
external force in and about Mz, Fx, and Fy directions are exerted
is improved as compared to conventional sensors. Note that the
present invention is not limited to the foregoing statements in
Embodiment 1, and various variations are available.
[0113] For example, the foregoing description discussed a case in
which the force sensor 1 is attached to an industrial robot arm;
however, needless to say, for example, besides the industrial robot
arm, the force sensor 1 can be used in applications such as tactile
sensing by a remote-controlled robot and detection of
resistance/external force exerted on wind tunnel test model.
Furthermore, according to the foregoing description, the base block
6 and the frame portion 11 of the strain element 10 of the force
sensor 1 are fixed, whereas the table block 2 and the central
portion 12 of the strain element 10 serve to receive an external
force (load). However, such conditions may be reversed so that the
table block 2 and the central portion 12 of the strain element 10
are fixed whereas the base block 6 and the frame portion 11 of the
strain element 10 serve to receive an external force and thereby
the force sensor 1 may be used in applications of measurement
subjects. Moreover, as the outer circumference of the central
portion 12, besides the shape of substantially a hexagon, some
other polygonal shape, circular shape, or the like shape may be
employed.
[0114] Furthermore, the foregoing manner in which the strain gauges
A1 to C4' are disposed on the arm portions 20 to 22 (see FIGS. 6
and 7) is an example, and, needless to say, some other manner of
disposition can be employed. For example, with regard to the strain
gauges A3 and A4 and the like disposed in the area close to the
frame portion 11, such strain gauges may be at an angle (at an
angle of 45 degrees to the center line Y10) so as to diverge away
from each other with decreasing distance to the frame portion 11,
instead of being disposed so as to diverge away from each other
with decreasing distance to the central portion 12 (see FIGS. 1 to
3 and 7 to 10 of Patent Literature 1). Furthermore, in the
foregoing descriptions, the strain gauges A1 to C4', which are of a
type in which a strain gauge main material is deposited on a base
material for a strain gauge, are bonded to the arm portions 20 to
22 with an adhesive. However, strain gauges made of a thin metal
film may be formed by directly or indirectly forming a film by
vacuum deposition, sputtering method, or the like on the front
faces and the back faces of the arm portions 20 to 22.
[0115] Moreover, a residual stress layer may be formed on the four
sides of each of the arm portions 20 to 22 by, instead of shot
peening by which a shot material is allowed to collide, laser
peening by which laser light (laser beam) is applied. Also in a
case of carrying out laser peening, masking for blocking laser is
put on the areas illustrated in FIG. 8 (cross-hatched areas).
However, in a case where an apparats capable of controlling the
range (area) irradiated with laser is used, masking is not
necessary, and laser peening is carried out by controlling the
apparatus so that laser is applied only to the four sides of each
of the arm portions 20 to 22.
[0116] Furthermore, the three through-openings 25, 26, and 27 in
the frame portion 11 may be omitted, provided that the condition is
such that the arm portions 20 to 22 are likely to elastically
deform near the frame portion 11. The condition in which the arm
portions 20 to 22 are likely to elastically deform is, for example,
a case in which the dimensions of the arm portions 20 to 22 in the
direction of their extension are long in relation to the diameter
of strain element 10, sizes of the first space 15 to the third
space 17 between the frame portion 11 and the central portion 12,
and the like. Other examples include a case in which the width of
each arm portion orthogonal to the direction of extension is small
and a case in which the thickness of each arm portion is small.
[0117] (a) and (b) of FIG. 12 illustrate a strain element 10' in
accordance with a variation. The strain element 10' in accordance
with the variation is the same in the main configuration and the
like as the foregoing strain element 10 illustrated in FIGS. 4 and
5, and includes a frame portion 11', a central portion 12', and arm
portions 20' to 22' (strain gauges are disposed on arm portions). A
difference is that the strain element 10' in accordance with the
variation does not have the through-openings 25, 26, and 27 of the
frame portion 11 illustrated in FIGS. 4 and 5 but has near-center
through-openings 50' to 52' (corresponding to second
through-openings) formed in the central portion 12'.
[0118] The near-center through-openings 50' to 52', in the central
portion 12', are provided between (i) locating through-holes 14a'
to 14c' provided in areas corresponding to the extensions of the
respective arm portions 20' to 22' extending toward the central
portion 12' and (ii) central junctions 20c' to 22c' where the
respective arm portions 20' to 22' connect to the central portion
12'. Each of the near-center through-openings 50' to 52' is in the
form of a straight line, and is in parallel to and slightly shorter
than a corresponding one of outer peripheral edge portions 12c',
12d', and 12e' which form the outer contour of the hexagonal
central portion 12'.
[0119] In the strain element 10' in accordance with the variation,
the central portion 12' has the foregoing near-center
through-openings 50' to 52', and thereby deformability of the arm
portions 20' to 22' in stretch directions corresponding to the
directions of extension of the arm portions 20' to 22' is reduced.
This makes it possible to ensure detection accuracy in the stretch
directions. Also, the central junctions 20c' to 22c', where the
respective arm portions 20' to 22' connect to the central portion
12', have a smaller rigidity than in the case of the strain element
10 illustrated in the drawings such as FIG. 4, and are capable of
sensitively detecting strain even when a load is small.
[0120] (a) and (b) of FIG. 13 illustrate a strain element 10'' in
accordance with another variation. The strain element 10'' in
accordance with another variation is the same in the main
configuration and the like as the strain element 10 illustrated in
FIGS. 4 and 5. Also, a frame portion 11'' has through-openings 25''
to 27'' corresponding to the through-openings 25 to 27 of the frame
portion 11 which are characteristic of the strain element 10. Also,
a central portion 12'' has near-center through-openings 50'' to
52'' corresponding to the near-center through-openings 50' to 52'
of the central portion 12' which are characteristic of the strain
element 10' of Variation 10 illustrated in (a) and (b) of FIG.
12.
[0121] The strain element 10'' has the through-openings 25'' to
27'' in the frame portion 11'' and has the near-center
through-openings 50'' to 52'' (second through-openings provided
between locating through-holes 14a'' to 14c'' and junctions where
the respective arm portions 20'' to 22'' connect to the central
portion 12'') in the central portion 12''. This achieves both the
advantage provided by the foregoing through-openings 25 to 27 of
the strain element 10 and the advantage provided by the near-center
through-openings 50' to 52' of the strain element 10'. This is
particularly preferable in a case where, for example, measurement
of a small external force is carried out. This is because the
strain element 10'' is arranged such that: the deformability of the
arm portions 20'' to 22'' in stretch directions corresponding to
the directions of extension of the arm portions 20'' to 22'' is
further reduced; and that the opposite ends of each of the arm
portions 20'' to 22'' are relatively smaller in rigidity and
elastically deform more sensitively in response to an external
force (load).
[0122] In the strain element 10 illustrated in FIGS. 4 and 5, in
the strain element 10' illustrated in FIG. 12, and in the strain
element 10'' illustrated in FIG. 13, the three locating
through-holes 14a to 14c, the three locating through-holes 14a' to
14c', and the three locating through-holes 14a'' to 14c'' are
provided in the central portions 12, 12', and 12'', respectively.
Note, however, that the number of locating through-holes can be
reduced to two, depending on specifications (for example, in the
strain elements 10, 10', and 10'', the locating through-holes 14c,
14c', and 14c'' can be omitted, respectively. See locating
through-holes 114a and 114b of a strain element 110 in accordance
with Embodiment 2 illustrated in FIGS. 19 and 20 described later).
As such, when the number of locating through-holes is two, it is
possible to, for example, reduce the number of processing areas and
the number of man-hours for assembly. Note that, in a case where
the number of locating through-holes of a strain element (for
example, strain element 10) is reduced, a locating through-hole
(for example, locating through-hole 4c) of the table block 2
corresponding to that omitted locating through-hole (for example,
locating through-hole 14c) is also omitted.
[0123] Moreover, in the above descriptions, the number of
hand-attaching screw holes for attachment of a robot hand to the
table block 2 is three in total (the hand-attaching screw holes 5a
to 5c). However, in a case where it is necessary to attach the
robot hand more firmly, four hand-attaching screw holes may be
provided in a circumferential direction so as to be spaced apart
from each other by 90 degrees (see hand-attaching screw
through-holes 105a to 105d of a table block 102 of the force sensor
101 in accordance with Embodiment 2 illustrated in FIG. 16
described later). Similarly, also with regard to the three
arm-attaching screw holes 7a to 7c for attachment of the base block
6 to the robot arm, in a case where it is necessary to attach the
base block 6 to the robot arm more firmly, four arm-attaching screw
holes may be provided in a circumferential direction so as to be
spaced apart from each other by 90 degrees.
[0124] (a) to (c) of FIG. 14 illustrate a variation of masking of
the strain element 10, in which non-masked portions are broader
than those of the masked strain element 10 illustrated in (a) to
(c) of FIG. 8. Specifically, areas including the outer peripheral
edge portions 12c, 12d, and 12e, where the respective central
junctions 20c to 22c (which are the central portion 12-side ends of
the respective arm portions 20 to 22) connect to the central
portion 12, are also left unmasked. These areas including the outer
peripheral edge portions 12c, 12d, and 12e, where the respective
central junctions 20c to 22c (which are the central portion 12-side
ends of the respective arm portions 20 to 22) connect to the
central portion 12, are areas in the form of straight lines
parallel to the edges corresponding to the outer peripheral edge
portions 12c, 12d, and 12e. Furthermore, areas including the inner
peripheral edge portions 11c, 11d, and 11e, where respective outer
junctions 20d to 22d (which are the frame portion 11-side ends of
the respective arm portions 20 to 22) connect to the frame portion
11 (such areas are areas in the form of straight lines parallel to
the edges corresponding to the inner peripheral edge portions 11c,
11d, and 11e), are also left unmasked.
[0125] Specifically, the central junctions 20c to 22c and the outer
junctions 20d to 22d, from which the arm portions 20 to 22 extend,
are likely to undergo stress concentration. Because of this, there
is a tendency that the vicinities of the outer peripheral edge
portions 12c, 12d, and 12e of the central portion 12, where the
respective central junctions 20c to 22c connect to the central
portion 12, and the vicinities of the inner peripheral edge
portions 11c, 11d, and 11e of the frame portion 11, where the
respective junctions 20d to 22d connect to the frame portion 11,
are also subjected to a large burden due to stress concentration.
To address this, the step of projecting a shot material at the
strain element 10 may be carried out under a condition in which, as
illustrated in (a) to (c) of FIG. 14, the areas including the outer
peripheral edge portions 12c, 12d, and 12e and the areas including
the inner peripheral edge portions 11c, 11d, and 11e are also left
unmasked. With this, a residual stress layer having negative
residual stress is formed also in the areas corresponding to these
edge portions, and the resistance to fatigue failure resulting from
elastic deformation can be further improved. Note that, in this
variation, the linear areas parallel to the edges corresponding to
the respective inner peripheral edge portions 11c to 11e and outer
peripheral edge portions 12c to 12e are also included in strain
portions in addition to the arm portions 20 to 22.
[0126] (a) to (c) of FIG. 15 illustrate another variation of
masking of the strain element 10, in which non-masked portions are
even broader than the variation illustrated in (a) to (c) of FIG.
14. Specifically, areas including corners of edges of the outer
peripheral edge portions 12c, 12d, and 12e, where the respective
central junctions 20c to 22c of the respective arm portions 20 to
22 connect to the central portion 12, are also left unmasked. These
areas including the corners of the edges of the outer peripheral
edge portions 12c, 12d, and 12e, where the respective central
junctions 20c to 22c of the respective arm portions 20 to 22
connect to the central portion 12, are areas each in the form of a
straight line including the opposite corners of the edge of a
corresponding one of the outer peripheral edge portions 12c, 12d,
and 12e. Furthermore, areas of the inner peripheral edge portions
11c, 11d, and 11e (where the outer junctions 20d to 22d of the
respective arm portions 20 to 22 connect to the frame portion 11),
corresponding to the regions in longitudinal directions of the
respective through-openings 25 to 27, are also left unmasked. These
areas of the inner peripheral edge portions 11c, 11d, and 11e
(where the respective outer junctions 20d to 22d of the respective
arm portions 20 to 22 connect to the frame portion 11),
corresponding to the regions in the longitudinal directions of the
respective through-openings 25 to 27, are areas in the form of
straight lines corresponding to the regions in the longitudinal
directions of the respective through-openings 25 to 27, near the
inner peripheral edge portions 11c, 11d, and 11e.
[0127] As described earlier with regard to the variation of masking
in (a) to (c) of FIG. 14, the vicinities of the outer peripheral
edge portions 12c, 12d, and 12e of the central portion 12 are
structurally subjected to a large burden due to stress
concentration. Similarly, the vicinities of the inner peripheral
edge portions 11c, 11d, and 11e of the frame portion 11 are likely
to undergo stress concentration due to the presence of the
through-openings 25 to 27 in the form of slots. To address this,
the step of projecting a shot material at the strain element 10 may
be carried out under a condition in which, as illustrated in (a) to
(c) of FIG. 15, the areas including corners of edges of the outer
peripheral edge portions 12c, 12d, and 12e are also left unmasked.
The step of projecting a shot material at the strain element 10 may
be carried out under a condition in which also the areas including
the regions of the inner peripheral edge portions 11c, 11d, and 11e
corresponding to the longitudinal directions of the
through-openings 25 to 27 are also left unmasked. With this, a
residual stress layer having negative residual stress is formed
also in these areas, and the resistance to fatigue failure
resulting from elastic deformation can be further improved. Note
that, in this variation, non-masked portions of the inner
peripheral edge portions 11c to 11e and outer peripheral edge
portions 12c to 12e are also included in strain portions.
Embodiment 2
[0128] FIGS. 16 to 18 illustrate a force sensor 101, which is a
specific example of a physical quantity measurement sensor in
accordance with Embodiment 2 of the present invention. The force
sensor 101 in accordance with Embodiment 2 is for application in an
industrial robot arm, similarly to the force sensor 1 in accordance
with Embodiment 1 illustrated in the drawings such as FIG. 1. Note,
however, that the force sensor 101 in accordance with Embodiment 2
is characterized as employing a strain element 110 (see FIGS. 17 to
20) which is a single member serving both as the strain element 10
and the base block 6 of the force sensor 1 in accordance with
Embodiment 1. The force sensor 101 in accordance with Embodiment 2,
which employs such a structure, thereby also achieves a reduction
in parts count, a reduction in the number of man-hours for
assembly, a reduction in dimension in the Z axis direction,
improvement in mountability of an electrical system board, and a
reduction in the number of man-hours for processing, as compared to
the force sensor 1 in accordance with Embodiment 1. The following
description will discuss the force sensor 101 in accordance with
Embodiment 2 in detail. Note that the X, Y, and Z axis directions
in Embodiment 2 are the same as those of Embodiment 1.
[0129] As illustrated in (a) and (b) of FIG. 17, the force sensor
101 is configured such that a table block 102 located on a
robot-hand side (front side) and a strain element 110 located on a
robot-arm side (back side) are stacked together.
[0130] The table block 102 is constituted by a disk-shaped member
having a certain thickness, is in the shape of a circle when viewed
from front side (see (a) of FIG. 16), and has many holes
(through-holes) in a flat front face 102a corresponding to the
front side. Specifically, the table block 102 has, in the vicinity
of the center of a circle, bolt through-holes 103a, 103b, and 103c
(countersunk through-holes for passage of bolts) which are arranged
to form an equilateral triangle symmetrical with respect to center
line Y2 in the height direction. Also, the table block 102 has
locating holes 104a and 104b (holes with fit tolerance) on the
left-hand side of the bolt through-hole 103a and below the bolt
through-hole 103a.
[0131] The table block 102 further has hand-attaching screw
through-holes 105a, 105b, 105c, and 105d (internally threaded
through-holes) which are arranged in the vicinity of the outer
circumference to substantially form a square. These hand-attaching
screw through-holes 105a, 105b, 105c, and 105d are used for
attachment to the robot hand. The table block 102 further has
hand-locating holes 104d and 104e on a horizontal line orthogonal
to the center line Y2 extending in the height direction such that
the hand-locating holes 104d and 104e are symmetrical with respect
to the center line Y2. These hand-locating holes 104d and 104e are
used for positioning relative to the robot hand. Furthermore, the
table block 102 is shaped such that, in the back face 102d, there
is a hollow 102c with a rim portion 102f remaining (see (b) of FIG.
17).
[0132] On the other hand, the strain element 110 is, as also
illustrated in FIGS. 19 and 20, constituted by a disk-shaped member
which is thicker than the strain element 10 in accordance with
Embodiment 1. The strain element 110 has a circular outer
circumference when seen front side (see (a) of FIG. 19) and from
back side (see FIG. 20), similarly to the strain element 10 in
accordance with Embodiment 1. The strain element 110 is structured
such that the central portion 112 and the frame portion 111
surrounding the central portion 112 are connected by three arm
portions 120, 121, and 122 (corresponding to strain portions) (see
(a) of FIG. 19 and FIG. 20). Note that the configurations of the
arm portions 120 to 122 are basically the same as those of
Embodiment 1, and elastically deform in response to an external
load or moment. The strain element 110 in accordance with
Embodiment 2 is characterized in that the dimension in the Z axis
direction (thickness) is greater than that of Embodiment 1 and that
the central portion 112 protrudes from the front face 110a of the
strain element 110. Another characteristic is, for example, the
back face 110b has a cavity 110e in the form of a recess in the
central area excluding the peripheral area.
[0133] The central portion 112 has screw through-holes 113a, 113b,
and 113c (internally threaded through-holes) which are arranged to
form an equilateral triangle and locating through-holes 114a and
114b (through-holes with fit tolerance) in the vicinities of
junctions where the central portion 112 connects to the respective
arm portions 120 and 121. The screw through-holes 113a to 113c
correspond to the foregoing bolt through-holes 103a to 103c of the
table block 102, whereas the locating through-holes 114a and 114b
correspond to the locating holes 104a and 104b of the table block
102. Furthermore, the central portion 112, whose outline is in the
shape of substantially a hexagon, is connected to the arm portions
120, 121, and 122 at middle portions of respective outer peripheral
edge portions 112c, 112d, and 112e, which are three of the six
edges of the hexagon and which do not face the screw through-holes
113a, 113b, and 113c.
[0134] The frame portion 111 has an outer contour in the form of a
circle, and an inner contour in the form of a hexagon which is
obtained by uniformly enlarging the contour of the foregoing
central portion 112. Furthermore, the frame portion 111 has bolt
through-holes 118a, 118b, 118c, and 118d which are arranged to from
a quadrangle. Furthermore, the frame portion 111 is connected to
the arm portions 120, 121, and 122 at middle portions of respective
inner peripheral edge portions 111c, 111d, and 111e located
opposite the respective outer peripheral edge portions 112c, 112d,
and 112e of the foregoing central portion 112. Because of the
presence of such arm portions 120, 121, and 122, the space between
the frame portion 111 and the central portion 112 is divided into
three, resulting in formation of a first space 115, a second space
116, and a third space 117.
[0135] The frame portion 111 further has three through-openings
125, 126, and 127 (each corresponding to first through-opening) in
the junctions where the frame portion 111 connects to the
respective arm portions 120 to 122. These through-openings 125 to
127 are in the shape of straight lines along the inner peripheral
edge portions 111c, 111d, and 111e at the inner circumference in
the form of a hexagon, and are equal to or slightly greater in
length than the edges of the respective inner peripheral edge
portions 111c, 111d, and 111e, similarly to the through-openings 25
to 27 of Embodiment 1.
[0136] Furthermore, as illustrated in FIG. 20, the strain element
110 has a hollow 110e, which is in a large circular shape, in the
central area when seen from the back face 110b. The hollow 110e has
a dimension in a radial direction that is long enough to include
the foregoing through-openings 125 to 127. Therefore, in the strain
element 110, a ring-shaped area including the arm portions 120 to
122 and the through-openings 125 to 127 in the frame portion 111
has the smallest thickness (dimension in the Z axis direction).
This thickness is the thickness from a bottom 110d of the hollow
110e to the front face 110a of the strain element 110. The second
thinnest is the thickness of the central portion 112. This
thickness is from the bottom 110d of the hollow 110e to a raised
face 112a of the central portion. The thickest is the thickness of
an outer circumference area (ring-shaped area) of the frame portion
111. This thickness is from the front face 110a of the strain
element 110 (identical to frame portion's front face 111a) to the
back face 110b of the strain element 110.
[0137] The strain element 110 in accordance with Embodiment 2 has
thicknesses as described above. This ensures, in the thinnest
ring-shaped area including the arm portions 120 to 122 and the
through-openings 125 to 127 of the frame portion 111, the ability
to easily elastically deform in response to an external load or
moment. Furthermore, the second thickest central portion 112
ensures rigidity that is necessary to function as, when the force
sensor 101 is combined with the foregoing table block 102, a force
receiver serving to receive an external force from the table block
102. Moreover, the outer circumference area (ring-shaped area) of
the frame portion 111, which is the thickest, is a portion directly
joined to the robot arm, and therefore has a thickness
corresponding to a rigidity required for operation of the robot
arm.
[0138] Note that the strain element 110 has, in the back face 110b
illustrated in FIG. 20, locating holes 119a and 119b for the robot
arm, in the outer circumference area of the frame portion 111.
Also, the strain element 110 has a recess 110f and a groove 110g
for passage of lead wires for connections of the electrical system
board accommodated in the hollow 110e. Moreover, a substrate
constituting an electrical signal processing module (see signal
processing module 30 in accordance with Embodiment 1 illustrated in
FIG. 10) is disposed in the hollow 110e of the finished strain
element 110. Also, lead wires for external connection, running from
the substrate, are accommodated and disposed in the groove 110g,
within the hollow 110e of the finished strain element 110. With
this, as illustrated in (b) of FIG. 16, the hollow 110e is closed
by attaching a circular cover 160 to the hollow 110e. Also, a
recess cover 107 is attached to the recess 110f, and thereby the
recess 110f and the groove 110g are closed.
[0139] The strain element 110 configured as described above has
been formed by machining (cutting) an elastically deformable metal
material, similarly to Embodiment 1, and corner easing to removed
burrs on peripheries, edges, corners, and the like of the strain
element 110 has also been carried out. With regard to this corner
easing, careful corner easing is carried out also with respect to
the strain element 110 in accordance with Embodiment 2, similarly
to Embodiment 1. The corner easing is carried out with respect to,
for example, corners of edges of junctions where the frame portion
11 and the respective arm portions 120 to 122 connect together,
corresponding to the areas enclosed by dot-dot-dash lines in FIGS.
6 and 7 of Embodiment 1. The corner easing is carried out also with
respect to corners of edges of junctions where the central portion
112 and the respective arm portions 120 and 122 connect together.
Note that the radius of curvature forming each of such corners, and
the like, are also the same as those of Embodiment 1. Furthermore,
when such machining and corner easing are carried out, also in
Embodiment 2, surface processing (processing by projecting shot
material) is to be carried out after masking.
[0140] FIG. 21 illustrates the strain element 110 (unfinished
strain element) which has been masked for surface processing. In
the masking step involving masking, as illustrated in FIG. 21, the
strain element 110 is masked by adhesive tape T except for the arm
portions 120 to 122 including areas for disposition of strain
gauges A11 to C14' (i.e., the strain element 110 is masked except
for strain portions. In Embodiment 2, the frame portion 111 and the
central portion 112 are masked). Note that side faces in the
thickness direction, such as outwardly facing faces of the central
portion 112, inwardly facing faces of the frame portion 111, and a
outwardly facing face 110c of the strain element 110 (frame portion
111), are also masked. Therefore, on each of the arm front faces
120a to 122 of the arm portions 120 to 122 which are left unmasked,
an area extending from a corresponding one of central junctions
120c to 122c (where the arm portion connects to the central portion
112) to a corresponding one of outer junctions 120d to 122d (where
the arm portion connects to the frame portion 111) is exposed.
Also, on each of the arm back faces 120b to 122b of the arm
portions 120 to 122 which are left unmasked, an area extending from
a corresponding one of central junctions 120c to 122c to a
corresponding one of outer junctions 120d to 122d (where the arm
portion connect to the frame portion 11) is exposed. Furthermore,
opposite side faces of each of the non-masked arm portions 120 to
122 are also exposed. Therefore, all four sides of each of the arm
portions 120 to 122 are exposed.
[0141] Then, similarly to Embodiment 1, the step of projecting a
shot material at the strain element 110 which has been masked,
illustrated in FIG. 21, is carried out, and thereby a residual
stress layer having compressive residual stress is formed in the
non-masked portions (strain portions). Moreover, the strain
portions in which such a residual stress layer is formed has a
surface roughness rougher than those of the non-masked areas.
[0142] When the step of projecting a shot material is completed as
described above, the masking material is removed, and then the
strain gauges A11 to C14' are bonded with an adhesive to the arm
front faces 120a to 122a and the arm back faces 120b to 122b of the
arm portions 120 to 122. The strain gauges A11 to C14' in
accordance with Embodiment 2 correspond to the strain gauges A1 to
C4' in accordance with Embodiment 1, and are the same as the strain
gauges A1 to C4' in accordance with Embodiment 1 in terms of the
manner in which the strain gauges A11 to C14' are disposed, the
manner in which they are bonded, the manner in which they are
electrically connected (see strain gauge circuit illustrated in
FIG. 9), and the like. Also, a signal processing module for
processing output voltage signal from a strain gauge circuit
constituted by connecting the strain gauges A11 to C14', in the
force sensor 101 in accordance with Embodiment 2, is also the same
as that used in Embodiment 1 (see FIG. 10).
[0143] With regard to the strain element 110 having gone through
such production steps, as described earlier, a substrate of an
electrical signal processing module is accommodated in the hollow
110e and the lead wires extending from the substrate are also
accommodated in the groove 110g, and then the hollow 110e and the
recess 110f are closed with the cover 106 and the recess cover 107.
Next, the following description discusses, with reference to FIGS.
17 and 18, a procedure by which the force sensor 101 constituted by
the strain element 110 and the table block 102 is attached to the
industrial robot arm.
[0144] First, as illustrated in (a) and (b) of FIG. 18, the strain
element 110 is attached to the robot arm-side of the industrial
robot arm. Before doing so, locating pins P2 are press-fit into the
locating holes 119a and 119b in the back face 110b of the strain
element 110. The tips of the locating pins P2 are press fit into
locating through-holes in the robot arm provided so as to
correspond to the locating holes 119a and 119b, and the back face
110b of the strain element 110 is placed on the end face at an end
portion of the robot arm (see (b) of FIG. 18). Then, bolts N2
(hexagon socket head bolts) are put through the four bolt
through-holes 118a to 118d in the front face 110a of the strain
element 110, and fastened to screw holes which are provided in the
robot arm so as to correspond to the bolt through-holes 118a to
118d. This fixes the strain element 110 to the robot arm (see (a)
of FIG. 18).
[0145] Next, the table block 102 is attached to the strain element
110 to assemble the force sensor 101. Specifically, locating pins P
are press fit into the locating holes 104a and 104b in the table
block 102 from the back face 102d, in advance. The tips of the
locating pins P are press fit into the locating through-holes 114a
and 114b which are provided in the raised face 112a of the central
portion 112 of the strain element 110 so as to correspond to the
locating holes 104a and 104b. The back face 102d of the table block
102 is placed on the raised face 112a of the central portion 112 of
the strain element 110 (see (b) of FIG. 17). Note that, in the
drawings such as (b) of FIG. 17, the covers 106 and 107 which cover
the hollow 110e and the recess 110f in the strain element 110 are
not illustrated.
[0146] Next, bolts N (hexagon socket head bolts) are put through
the three bolt through-holes 103a to 103c in the front face 102a of
the table block 102. The bolts N are fastened to the three screw
through-holes 113a, 113b, and 113c which are provided in the raised
face 112a of the central portion 112 of the strain element 110 so
as to correspond to the bolt through-holes 103a to 103c. With this,
the table block 102 is fixed to the strain element 110, and thereby
the force sensor 101 in accordance with Embodiment 2 is
completed.
[0147] Note that, with regard to a procedure by which the robot
hand-side of the industrial robot arm is attached to the force
sensor 101, locating pins P1 are press-fit into locating holes in
the robot hand in advance. The tips of such locating pins P1 are
press-fit into the hand-locating holes 104d and 104e in the front
face 102a of the table block 102. The robot hand is placed on the
front face 102a of the table block 102 (see (b) of FIG. 18). Then,
bolts Ni (hexagon socket head bolts) are put through the four bolt
through-holes in the robot hand, and fastened to the four
hand-attaching screw through-holes 105a, 105b, 105c, and 105d in
the front face 102a of the table block 102. This fixes the robot
hand to the table block 102.
[0148] According to the force sensor 101 in accordance with
Embodiment 2 configured as described above, a load against the
robot hand is first exerted on the table block 102. The load
exerted on the table block 102 is received, as an external force,
by the central portion 112 of the strain element 110 whose raised
face 112a is in contact with the back face 102d of the table block
102. Upon receipt of the external force by the central portion 112
of the strain element 110, the arm portions 120 to 122, which
connect the central portion 112 and the frame portion 111 fixed to
the robot arm, elastically deform, and the strain gauges A11 to
C14' carry out detection of strain associated with such elastic
deformation.
[0149] Furthermore, also in the frame portion 111 included in the
force sensor 101 in accordance with Embodiment 2, a residual stress
layer having compressive residual stress is formed on each of the
arm portions 120 to 122. Therefore, metal fatigue strength
associated with elastic deformation is improved. Moreover, since
stress concentration is reduced in corner portions at edges of
junctions where the respective arm portions 120 to 122 connect to
the frame portion 111 and in corner portions at edges of junctions
where the respective arm portions 120 to 122 connect to the central
portion 112, working life can be prolonged. Moreover, Embodiment 2,
which employs the frame portion 111 configured as described above,
thereby achieves, in addition to the effects which are the same as
the above-mentioned effects of Embodiment 1, a reduction in parts
count, a reduction in the number of man-hours for assembly, a
reduction in dimension in the Z axis direction, improvement in
mountability of electrical system board, and a reduction in the
number of man-hours for processing.
[0150] Note that, also in Embodiment 2, the adhesiveness of the
strain gauges A11 to C14' disposed on the arm portions 120 to 122
is increased, and therefore measurement accuracy is also improved
as compared to conventional techniques. Note that, also in
Embodiment 2, various variations described earlier in Embodiment 1
can be employed.
[0151] FIGS. 22 and 23 illustrate variations of masking of the
strain element 110 in accordance with Embodiment 2. (a) to (c) of
FIG. 22 correspond to the variation of masking in accordance with
Embodiment 1 described with reference to (a) to (c) of FIG. 14. (a)
to (c) of FIG. 23 correspond to the another variation of masking in
accordance with Embodiment 1 described with reference to (a) to (c)
of FIG. 15. Each variation shows a state in which each non-masked
area illustrated in FIG. 21 has been broadened from the opposite
ends of each of the arm portions 120 to 122.
[0152] Specifically, in the variation of masking illustrated in (a)
to (c) of FIG. 22, areas including the outer peripheral edge
portions 112c, 112d, and 112e, where the respective central
junctions 120c to 122c (which are the central portion 112-side ends
of the respective arm portions 120 to 122) connect to the central
portion 112, are also left unmasked. These areas including the
outer peripheral edge portions 112c, 112d, and 112e, where the
respective central junctions 120c to 122c (which are the central
portion 112-side ends of the respective arm portions 120 to 122)
connect to the central portion 112, are areas in the form of
straight lines parallel to the edges corresponding to the outer
peripheral edge portions 112c, 112d, and 112e. Furthermore, areas
including inner peripheral edge portions 111c, 111d, and 111e,
where respective outer junctions 120d to 122d (which are the frame
portion 111-side ends of the respective arm portions 120 to 122)
connect to the frame portion 111, are also left unmasked. The areas
including the inner peripheral edge portions 111c, 111d, and 111e,
where the respective outer junctions 120d to 122d (which are the
frame portion 111-side ends of the respective arm portions 120 to
122) connect to the frame portion 111, are areas in the form of
straight lines parallel to the edges corresponding to the inner
peripheral edge portions 111c, 111d, and 111e.
[0153] The central junctions 120c to 122c and the outer junctions
120d to 122d, from which such arm portions 120 to 122 extend, are
likely to undergo stress concentration. Because of this, there is a
tendency that the vicinities of the outer peripheral edge portions
112c, 112d, and 112e of the central portion 112, where the
respective central junctions 120c to 122c connect to the central
portion 112, and the vicinities of the inner peripheral edge
portions 111c, 111d, and 111e of the frame portion 111, where the
respective junctions 120d to 122d connect to the frame portion 111,
are also subjected to a large burden due to stress concentration.
To address this, the step of projecting a shot material at the
strain element 110 may be carried out under a condition in which,
as illustrated in (a) to (c) of FIG. 22, the areas including the
outer peripheral edge portions 112c, 112d, and 112e and the areas
including the inner peripheral edge portions 111c, 111d, and 111e
are also left unmasked. With this, a residual stress layer having
negative residual stress is formed also in the areas corresponding
to these edge portions, and the resistance to fatigue failure
resulting from elastic deformation can be further improved. Note
that, in this variation, the linear areas parallel to the edges
corresponding to the respective inner peripheral edge portions 111c
to 111e and outer peripheral edge portions 112c to 112e are also
included in strain portions in addition to the arm portions 120 to
122.
[0154] In the another variation of masking illustrated in (a) to
(c) of FIG. 23, areas including corners of edges of the outer
peripheral edge portions 112c, 112d, and 112e, where the respective
central junctions 120c to 122c of the respective arm portions arm
portions 120 to 122 connect to the central portion 112, are also
left unmasked. These areas including the corners of the edges of
the outer peripheral edge portions 112c, 112d, and 112e, where the
respective central junctions 120c to 122c of the respective arm
portions 120 to 122 connect to the central portion 112, are areas
each in the form of a straight line including the opposite corners
of the edge of a corresponding one of the outer peripheral edge
portions 112c, 112d, and 112e. Areas of the inner peripheral edge
portions 111c, 111d, and 111e (where the respective outer junctions
120d to 122d of the respective arm portions 120 to 122 connect to
the frame portion 111), corresponding to the regions in
longitudinal directions of the respective through-openings 125 to
127, are also left unmasked. These areas of the inner peripheral
edge portions 111c, 111d, and 111e, corresponding to the regions in
the longitudinal directions of the respective through-openings 125
to 127, are areas in the form of straight lines corresponding to
the ranges in the longitudinal directions of the respective
through-openings 125 to 127, near the inner peripheral edge
portions 111c, 111d, and 111e.
[0155] As described earlier, the vicinities of the outer peripheral
edge portions 112c, 112d, and 112e of the central portion 112 are
structurally subjected to a large burden due to stress
concentration. Similarly, the vicinities of the inner peripheral
edge portions 111c, 111d, and 111e of the frame portion 111 are
likely to undergo stress concentration due to the presence of the
through-openings 125 to 127 in the form of slots. To address this,
the step of projecting a shot material at the strain element 110
may be carried out under a condition in which, as illustrated in
(a) to (c) of FIG. 23, the areas including corners of edges of the
outer peripheral edge portions 112c, 112d, and 112e are also left
unmasked. The step of projecting a shot material at the strain
element 110 may be carried out under a condition in which also the
areas including the regions of the inner peripheral edge portions
111c, 111d, and 111e corresponding to the longitudinal directions
of the through-openings 125 to 127 are also left unmasked. With
this, a residual stress layer having negative residual stress is
formed also in these areas, and the resistance to fatigue failure
resulting from elastic deformation can be further improved. Note
that, in this variation, non-masked areas of the inner peripheral
edge portions 111c to 111e and the outer peripheral edge portions
112c to 112e are also included in strain portions.
Embodiment 3
[0156] (a) to (c) of FIG. 24 illustrate a strain element 55 in
accordance with Embodiment 3 of the present invention, which is for
application to a load cell (load converter and force converter) as
a physical quantity measurement sensor. The strain element 55 in
accordance with Embodiment 3 is constituted by a cylindrical member
56. The strain element 55 is configured such that, on its front
side 56a of the outer circumferential surface extending from top to
bottom beyond center line X5 parallel to the X axis direction
(horizontal direction), areas each intersecting center line Y5
parallel to the Y axis direction (vertical direction) (i.e., a
front-side upper area 56c and a front-side lower area 56d) are used
as areas for attachment of strain gauges. The strain element 55 is
also configured such that, on its back side 56b of the outer
circumferential surface extending from top to bottom beyond the
center line X5 parallel to the X axis direction, areas each
intersecting the center line Y5 parallel to the Y axis direction
(i.e., a back-side upper area 56e and a back-side lower area 56f)
are used as areas for attachment of strain gauges. These areas for
attachment of the strain gauges are four quadrangular regions
cross-hatched in (b) and (c) of FIG. 24.
[0157] Note that each area (the front-side upper area 56c, the
front-side lower area 56d, the back-side upper area 56e, and the
back-side lower area 56f) is in the shape of a quadrangle
(rectangle), and, while the longitudinal directions of the
front-side upper area 56c and the back-side upper area 56e are
parallel to the center line Y5, the longitudinal directions of the
front-side lower area 56d and the back-side lower area 56f are
parallel to the center line X5. Also in Embodiment 3, the main
material for the strain element 55, specifications of strain
gauges, the manner in which the strain gauges are disposed, and the
like are the same as those of Embodiment 1.
[0158] (a) to (c) of FIG. 25 illustrate the strain element 55 in
accordance with Embodiment 3 which has been masked. Also in the
production of the strain element 55 in accordance with Embodiment
3, the foregoing cylindrical member 56 is made from a material by
machining (including corner easing), and then, as illustrated in
(a) to (c) of FIG. 25, the member 56 is masked. Specifically,
assume that the quadrangular regions including the front-side upper
area 56c, the front-side lower area 56d, the back-side upper area
56e, and the back-side lower area 56f, which are areas for
attachment of strain gauges, are a front-side upper strain portion
56r, a front-side lower strain portion 56s, a back-side upper
strain portion 56t, and a back-side lower strain portion 56u,
respectively. These strain portions, which correspond to regions
subject to strain associated with elastic deformation under a load
(such strain portions are the front-side upper strain portion 56r,
the front-side lower strain portion 56s, the back-side upper strain
portion 56t, and the back-side lower strain portion 56u), are left
unmasked, and portions other than these strain portions (the
front-side upper strain portion 56r, the front-side lower strain
portion 56s, the back-side upper strain portion 56t, and the
back-side lower strain portion 56u) are masked. Note that the
masked areas are the areas cross-hatched in (a) to (c) of FIG.
25.
[0159] The strain portions (the front-side upper strain portion
56r, the front-side lower strain portion 56s, the back-side upper
strain portion 56t, and the back-side lower strain portion 56u),
which are left unmasked, are regions obtained by uniformly
enlarging, about 1.5- to 4-fold, the front-side upper area 56c, the
front-side lower area 56d, the back-side upper area 56e, and the
back-side lower area 56f which are areas for disposition of strain
gauges, respectively. In this example, the strain portions which
are left unmasked are about 2-fold enlarged regions. Note that the
masked areas of the strain element 55 are the front side 56a and
the back side 56b of the outer circumferential surface (side
surface) and circular top and bottom faces 56g and 56h of the
member 56 excluding the strain portions (the front-side upper
strain portion 56r, the front-side lower strain portion 56s, the
back-side upper strain portion 56t, and the back-side lower strain
portion 56u).
[0160] With respect to the strain element 55 which has been masked,
shot peening or laser peening is carried out. By such peening, a
residual stress layer having negative residual stress is formed in
each of the strain portions (the front-side upper strain portion
56r, the front-side lower strain portion 56s, the back-side upper
strain portion 56t, and the back-side lower strain portion 56u).
With this, even when the strain portions (the front-side upper
strain portion 56r, the front-side lower strain portion 56s, the
back-side upper strain portion 56t, and the back-side lower strain
portion 56u) of the front side 56a and the back side 56b
elastically deform in response to an external force (load), the
strain portions are resistant to fatigue failure resulting from
metal fatigue. Furthermore, in a case where shot peening involving
projecting a shot material is carried out as peening, the strain
portions (the front-side upper strain portion 56r, the front-side
lower strain portion 56s, the back-side upper strain portion 56t,
and the back-side lower strain portion 56u) are given a surface
roughness rougher than those of other portions. Therefore, even in
a case where the strain gauges are disposed by bonding with an
adhesive, the strain gauges have improved adhesiveness and become
better at conforming to elastic deformation, and the accuracy of
strain detection can be maintained. Note that, also in Embodiment
3, the variations described earlier in the embodiments such as
Embodiment 1 may be used if applicable.
Embodiment 4
[0161] (a) and (b) of FIG. 26 illustrate a strain element 60 in
accordance with Embodiment 4 of the present invention, which is for
application to a load cell (load converter and force converter) as
a physical quantity measurement sensor similarly to the foregoing
Embodiment 3. The strain element 60 in accordance with Embodiment 4
is constituted by a cube-shaped member 61, and has a hollow
extending through the member 61 from a front face 61b to a back
face 61d. The hollow, when seen from the front face 61b illustrated
in (b) of FIG. 26, is constituted by (i) a left through-opening 62
and a right through-opening 63 each in the form of a circle and
(ii) a connecting through-opening 64 which connects the left
through-opening 62 and the right through-opening 63. Since the
hollow constituted by such through-openings (the left
through-opening 62, the right through-opening 63, and the
connecting through-opening 64) is formed, when a top face 61a or a
bottom face 61c of the cube-shaped member 61 receives a load, the
top face 61a or the bottom face 61c elastically deforms. For
carrying out detection of strain associated with such elastic
deformation, the top face 61a and the bottom face 61c are provided
with areas for disposition of strain gauges.
[0162] Specifically, on the top face 61a of the member 61, a top
left area 65a and a top right area 65b, which are arranged along
center line X8 parallel to the X axis direction (horizontal
direction) and which correspond to the left through-opening 62 and
the right through-opening 63, are used as areas for attachment of
strain gauges. Furthermore, on the bottom face 61c, a bottom left
area 65c and a bottom right area 65d, which are arranged along the
center line X8 parallel to the X axis direction and which
correspond to the left through-opening 62 and the right
through-opening 63, are used as areas for attachment of strain
gauges (four quadrangular regions cross-hatched in (a) and (b) of
FIG. 26). Note that the areas (the top left area 65a, the top right
area 65b, the bottom left area 65c, and the bottom right area 65d)
are each in the shape of a quadrangle (rectangle), and their
longitudinal directions are each parallel to the center line X8.
Also in Embodiment 4, the main material for the strain element 60,
specifications of strain gauges, the manner in which the strain
gauges are disposed, and the like are the same as those of
Embodiment 1.
[0163] (a) to (c) of FIG. 27 illustrate the strain element 60 in
accordance with Embodiment 4 which has been masked. Also in the
production of the strain element 60 in accordance with Embodiment
4, first, the cube-shaped member 61 having the hollow constituted
by the through-openings (the left through-opening 62, the right
through-opening 63, and the connecting through-opening 64) is made
from a material by machining (including corner easing). Then, as
illustrated in (a) to (c) of FIG. 27, the member 61 is masked.
Specifically, quadrangular regions including the top left area 65a,
the top right area 65b, the bottom left area 65c, and the bottom
right area 65d, which are areas for attachment of strain gauges and
are referred to as a top left strain portion 61r, a top right
strain portion 61s, a bottom left strain portion 61t, and a bottom
right strain portion 61u, respectively, are left unmasked. Portions
other than these strain portions, which correspond to regions
subject to strain associated with elastic deformation under a load
(such strain portions are the top left strain portion 61r, the top
right strain portion 61s, the bottom left strain portion 61t, and
the bottom right strain portion 61u), are masked (masked areas are
the areas cross-hatched in (a) to (c) of FIG. 27).
[0164] The strain portions (the top left strain portion 61r, the
top right strain portion 61s, the bottom left strain portion 61t,
and the bottom right strain portion 61u), which are left unmasked,
are regions obtained by uniformly enlarging, about 1.5- to 4-fold,
the top left area 65a, the top right area 65b, the bottom left area
65c, and the bottom right area 65d, respectively, which are areas
for disposition of strain gauges. In this Example, the strain
portions which are left unmasked are about 2-fold enlarged regions.
Note that the masked areas of the strain element 60 are outer
surfaces of the member 61 excluding the foregoing strain portions
(the top left strain portion 61r, the top right strain portion 61s,
the bottom left strain portion 61t, and the bottom right strain
portion 61u). The outer surfaces are the top face 61a, the front
face 61b, the bottom face 61c, the back face 61d, a left side face
61e, a right side face 61f, and inner walls of the through-openings
(the left through-opening 62, the right through-opening 63, and the
connecting through-opening 64) constituting the hollow.
[0165] With respect to the strain element 60 which has been masked,
shot peening or laser peening is carried out. By such peening, a
residual stress layer having negative residual stress is formed in
each of the strain portions (the top left strain portion 61r, the
top right strain portion 61s, the bottom left strain portion 61t,
and the bottom right strain portion 61u). With this, even when the
strain portions (the top left strain portion 61r, the top right
strain portion 61s, the bottom left strain portion 61t, and the
bottom right strain portion 61u) of the top face 61a and the bottom
face 61c elastically deform in response to an external force
(load), the strain portions are resistant to fatigue failure
resulting from metal fatigue. Furthermore, in a case where shot
peening involving projecting a shot material is carried out as
peening, the strain portions (the top left strain portion 61r, the
top right strain portion 61s, the bottom left strain portion 61t,
and the bottom right strain portion 61u) are given a surface
roughness rougher than those of other portions. Therefore, even in
a case where the strain gauges are disposed by bonding with an
adhesive, the strain gauges have improved adhesiveness and become
better at conforming to elastic deformation, and the accuracy of
strain detection can be maintained. Note that, also in Embodiment
4, the variations described earlier in the embodiments such as
Embodiment 1 may be used if applicable.
Embodiment 5
[0166] (a) to (c) of FIG. 28 illustrate a strain element 70 in
accordance with Embodiment 5 of the present invention, which is for
application to a torque sensor as a physical quantity measurement
sensor. The strain element 70 in accordance with Embodiment 5
includes, similarly to the strain element 10 in accordance with
Embodiment 1, a frame portion 71 having a circular circumferential
outline when seen from front, and includes a central portion 72
(having a circular outline when seen from front side) which is
located in the space defined by the frame portion 71 such that
there are spaces 78a to 78d between the frame portion 71 and the
central portion 72. The strain element 70 is characterized in that
four arm portions 73 to 76, which connect the frame portion 71 and
the central portion 72, are arranged in a circumferential direction
so as to be spaced apart from each other by 90 degrees. Note that,
in (a) to (c) of FIG. 28, bolt holes, locating through-holes, and
the like illustrated in the drawings such as FIGS. 4 and 5 are not
illustrated, for clear illustration of the configuration of main
parts of the strain element 70.
[0167] According to the foregoing strain element 10 in accordance
with Embodiment 1, the thickness (dimension in Z axis direction) is
substantially the same among the frame portion 11, the central
portion 12, and the arm portions 20 to 22. However, according to
the strain element 70 in accordance with Embodiment 5, the
thicknesses of the frame portion 71 and the central portion 72 are
greater, because, for example, the strain element 70 is for
application to a torque sensor. Therefore, the thicknesses of the
arm portions 73 to 76 are less than those of the frame portion 71
and the central portion 72 (see (b) and (c) of FIG. 28).
[0168] Areas of the strain element 70 for disposition of strain
gauges are opposite side faces 73a and 73b of the arm portion 73
extending parallel to the Y axis direction and opposite side faces
75a and 75b of the arm portion 75 extending parallel to the Y axis
direction. With regard to the areas of the strain element 70 for
disposition of strain gauges, specifically, the regions
cross-hatched in (a) and (b) of FIG. 28 are areas 73e, 73f, 75e,
and 75f for disposition of strain gauges. Note that, in Embodiment
5, the main material for the strain element 70, specifications of
strain gauges, the manner in which the strain gauges are disposed,
and the like are the same as those of Embodiment 1.
[0169] (a) to (c) of FIG. 29 illustrate the strain element 70 in
accordance with Embodiment 5 which has been masked. Also in the
production of the strain element 70 in accordance with Embodiment
5, with respect to the strain element 70 which has been made into
the shape illustrated in (a) to (c) of FIG. 29 from a material by
machining (including corner easing), masking is carried out to mask
the regions cross-hatched in (a) to (c) of FIG. 29. These regions
are portions other than the opposite side faces 73a and 73b of the
arm portion 73 extending parallel to the Y axis direction and the
opposite side faces 75a and 75b of the arm portion 75 extending
parallel to the Y axis direction including the foregoing areas 73e,
73f, 75e, and 75f for disposition of strain gauges (the side faces
73a and 73b and the side faces 75a and 75b correspond to strain
portions corresponding to regions subject to strain).
[0170] Each of the non-masked opposite side faces 73a and 73b of
the arm portion 73 is a region extending from a junction 73c where
the arm portion 73 connects to the frame portion 71 to a junction
73d where the arm portion 73 connects to the central portion 72 in
the direction of extension of the arm portion 73 (the direction
parallel to the Y axis), and each of the non-masked opposite side
faces 75a and 75b of the arm portion 75 is a region extending from
a junction 75c where the arm portion 75 connects to the frame
portion 71 to a junction 75d where the arm portion 75 connects to
the central portion 72 in the direction of extension of the arm
portion 75 (the direction parallel to the Y axis). Note that the
masked areas are the whole circumferences of the frame portion 71
and the central portion 72, four sides of each of the arm portions
74 and 76 extending parallel to the X axis direction, and surfaces
of the arm portions 73 and 75 excluding the opposite side faces 73a
and 73b of the arm portion 73 extending parallel to the Y axis
direction and the opposite side faces 75a and 75b of the arm
portion 75 extending parallel to the Y axis direction.
[0171] With respect to the strain element 70 which has been masked,
shot peening or laser peening described in Embodiment 1 is carried
out. By such peening, a residual stress layer having negative
residual stress is formed on the opposite side faces 73a and 73b of
the arm portion 73 and the opposite side faces 75a and 75b of the
arm portion 75 including the areas 73e, 73f, 75e, and 75f for
disposition of strain gauges. With this, even when the opposite
side faces 73a and 73b of the arm portion 73 and the opposite side
faces 75a and 75b of the arm portion 75 elastically deform in
response to an external force (load), these faces are resistant to
fatigue failure resulting from metal fatigue.
[0172] Furthermore, in a case where shot peening involving
projecting a shot material is carried out as peening, the opposite
side faces 73a and 73b of the arm portion 73 and the opposite side
faces 75a and 75b of the arm portion 75 are given a surface
roughness rougher than those of other portions. Therefore, even in
a case where the strain gauges are disposed on the opposite side
faces 73a and 73b and the opposite side faces 75a and 75b by
bonding, the strain gauges become better at conforming to elastic
deformation of the arm portions 73 and 75, and the accuracy of
strain detection can be maintained.
[0173] Note that, also in Embodiment 5, various variations are
available. For example, depending on the purpose of use or the
like, the number of arm portions can be more than four.
Furthermore, arm portions can be unequally spaced apart from each
other in the circumferential direction instead of being equally
spaced. Moreover, the shape of the outline of the strain element
may be a polygon such as a quadrangle instead of a circle. Note
that, also in Embodiment 5, the variations described earlier in
Embodiment 1 can be employed.
Embodiment 6
[0174] (a) to (c) of FIG. 30 illustrate a strain element 80 in
accordance with Embodiment 6 of the present invention, which is for
application to a load cell as a physical quantity measurement
sensor. The strain element 80 in accordance with Embodiment 6 is
constituted by a frame part 81 having a circular (ring-shaped)
outline when seen from front. The strain element 80 is arranged
such that opposite ends 81c and 81d of an outer circumferential
face 81b, intersecting center line X10 (horizontal line H10 in side
view) parallel to the X axis direction (horizontal direction) (such
ends are hereinafter referred to as outer-circumferential
horizontal ends 81c and 81d), and opposite ends 81e and 81f of an
inner circumferential face 81a, intersecting the center line X10
(such ends are hereinafter referred to as inner-circumferential
horizontal ends 81e and 81f), i.e., four areas in total, are areas
for attachment of strain gauges (areas 81g, 81h, 81i, and 81j). The
areas 81g, 81h, 81i, and 81j for disposition of strain gauges are
the regions cross-hatched in (a) to (c) of FIG. 30. Note that, also
in Embodiment 6, the main material for the strain element 80,
specifications of strain gauges, and the like are the same as those
of Embodiment 1. The manner in which the strain gauges are disposed
is the same as those (including variations) described in Embodiment
1. The strain gauges can be disposed such that their detection
directions are each parallel to the Y axis direction.
[0175] (a) to (c) of FIG. 31 illustrate the strain element 80 in
accordance with Embodiment 6 which has been masked. Also in the
production of the strain element 80 in accordance with Embodiment
6, a material is made into the strain element 80 having the shape
illustrated in (a) to (c) of FIG. 31 by machining (including corner
easing). With regard to the strain element 80, the regions
cross-hatched in (a) to (c) of FIG. 31 are masked. These regions
are portions other than quadrangular outer-circumferential strain
portions 81r and 81s and inner-circumferential strain portions 81t
and 81u including the respective areas 81g, 81h, 81i and 81j for
disposition of strain gauges at the outer-circumferential
horizontal ends 81c and 81d intersecting the center line X10 and
the inner-circumferential horizontal ends 81e and 81f intersecting
the center line X10.
[0176] The outer-circumferential strain portions 81r and 81s and
the inner-circumferential strain portions 81t and 81u
(corresponding to strain portions corresponding to regions subject
to strain), which are left unmasked, are regions obtained by
uniformly enlarging, about 1.5- to 4-fold, the areas 81g, 81h, 81i,
and 81j for disposition of strain gauges, respectively. In this
Example, the strain portions which are left unmasked are about
2-fold enlarged regions. Note that the masked areas of the strain
element 80 are all the faces of the frame part 81 excluding the
foregoing outer-circumferential strain portions 81r and 81s and the
inner-circumferential strain portions 81t and 81u.
[0177] With respect to the strain element 80 which has been masked,
shot peening or laser peening is carried out. By such peening, a
residual stress layer having negative residual stress is formed in
the outer-circumferential strain portions 81r and 81s and the
inner-circumferential strain portions 81t and 81u including the
areas 81g, 81h, 81i, and 81j for disposition of strain gauges. With
this, even when the outer-circumferential strain portions 81r and
81s and the inner-circumferential strain portions 81t and 81u of
the frame part 81 elastically deform in response to an external
force (load), the strain portions are resistant to fatigue failure
resulting from metal fatigue.
[0178] Furthermore, in a case where shot peening involving
projecting a shot material is carried out as peening, the
outer-circumferential strain portions 81r and 81s and the
inner-circumferential strain portions 81t and 81u of the frame part
81 are given a surface roughness rougher than those of other
portions. Therefore, even in a case where the strain gauges are
disposed by bonding, the strain gauges become better at conforming
to elastic deformation of the outer-circumferential strain portions
81r and 81s and the inner-circumferential strain portions 81t and
81u of the frame part 81, and the accuracy of strain detection can
be maintained. Note that, also in Embodiment 6, the variations
described earlier in Embodiment 1 can be employed.
Embodiment 7
[0179] (a) to (c) of FIG. 32 illustrate a strain element 90 in
accordance with Embodiment 7 of the present invention, which is for
application to a load cell as a physical quantity measurement
sensor. In the strain element 90 in accordance with Embodiment 7, a
protruding portion 92 protruding in the form of a cylinder is
provided at the center of a top end face 94 of a short-length
cylindrical base portion 91. Also, the strain element 90 has a
hollow 93 in the bottom face opposite the end face 94. The strain
element 90 is configured such that four areas on an inner face 95,
which is the ceiling of the hollow 93 and which is opposite the end
face 94, are used as areas 96 to 99 for disposition of strain
gauges. The four areas are arranged along center line X20 (in the X
axis direction) and center line Y20 (in the Y axis direction) each
passing through a center 95a of the inner face 95, and are each
distant from the center 95a. The areas 96 to 99 for disposition of
strain gauges are the regions cross-hatched in (a) to (c) of FIG.
32. Note that, also in Embodiment 7, the main material for the
strain element 90, specifications of strain gauges, the manner in
which the strain gauges are disposed, and the like are the same as
those of Embodiment 1.
[0180] (a) to (c) of FIG. 33 illustrate the strain element 90 in
accordance with Embodiment 7 which has been masked. Also in the
production of the strain element 90 in accordance with Embodiment
7, a material is made into the strain element 90 having the shape
illustrated in (a) to (c) of FIG. 33 by machining (including corner
easing). This strain element is masked except for quadrangular
strain portions 90a to 90d including the respective areas 96 to 99
for disposition of strain gauges (masked areas are the regions
cross-hatched in (a) and (b) of FIG. 33).
[0181] The strain portions 90a to 90d (corresponding to strain
portions in accordance with an aspect of the present invention),
which are left unmasked, are regions obtained by uniformly
enlarging (about 1.5- to 4-fold) the areas 96 to 99 for disposition
of strain gauges. In this example, the strain portions which are
left unmasked are about 2-fold enlarged regions. Note that the
masked areas of the strain element 90 are all the faces of the base
portion 91 and the protruding portion 92 excluding the foregoing
quadrangular strain portions 90a to 90d.
[0182] With respect to the strain element 90 which has been masked,
shot peening or laser peening is carried out. By such peening, a
residual stress layer having negative residual stress is formed in
the quadrangular strain portions 90a to 90d including the
respective areas 96 to 99 for disposition of strain gauges. With
this, even when the end face 94 and the inner face 95 of the base
portion 91 elastically deform in response to an external force
(load), the faces are resistant to fatigue failure resulting from
metal fatigue.
[0183] Furthermore, in a case where shot peening involving
projecting a shot material is carried out as peening, the
quadrangular strain portions 90a to 90d are given a surface
roughness rougher than those of other portions. Therefore, even in
a case where the strain gauges are disposed by bonding, the strain
gauges become better at conforming to elastic deformation of the
end face 94 and the inner face 95 of the base portion 91, and the
accuracy of strain detection can be maintained. Note that, also in
Embodiment 7, the variations described earlier in Embodiment 1 can
be employed.
[0184] Aspects of the present invention can also be expressed as
follows.
[0185] An aspect of the present invention is directed to a strain
element which is elastically deformable in response to a load and
which is configured to have a strain gauge disposed thereon, the
strain gauge being configured to detect strain associated with
deformation, the strain element including a strain portion which
corresponds to a region subject to strain and which includes an
area for disposition of the strain gauge, the strain portion being
provided with a residual stress layer having negative residual
stress.
[0186] According to an aspect of the present invention, a residual
stress layer having negative residual stress (compressive residual
stress) has been formed in a strain portion which is in a region
where the strain element elastically deforms and which includes an
area for disposition of the strain gauge. Therefore, the resistance
to fatigue failure in the portion that elastically deforms, in
which the strain gauge carries out detection, increases. Since the
resistance to fatigue failure increases like this, a physical
quantity measurement sensor including the strain element can be
used stably over a long period of time. Note that the residual
stress layer may be formed by, for example, causing a shot material
to collide with the surface of the strain portion or irradiating
the surface of the strain portion with laser.
[0187] An aspect of the present invention is arranged such that the
strain portion has a surface roughness rougher than a portion other
than the strain portion.
[0188] According to an aspect of the present invention, the strain
portion, which includes the area for disposition of the strain
gauge, has a surface roughness greater than a portion other than
the strain portion. Therefore, the surface area of the strain
portion where an adhesive makes contact with the strain portion
increases, and, in a case where the strain gauge is bonded to the
strain element with an adhesive or the like, the adhesiveness to
the surface of the strain element (surface of the strain portion)
increases, and the strain gauge is firmly bonded. Because of this,
even when the strain element elastically deforms, the strain gauge
firmly bonded to the surface of the strain element with the
adhesive better conforms to the deformation, and the accuracy of
strain detection can be increased as compared to conventional
techniques.
[0189] An aspect of the present invention includes: a frame
portion; a central portion which is located in a space defined by
the frame portion so as to be spaced apart from the frame portion;
and an arm portion which connects the frame portion with the
central portion and which corresponds to the strain portion, and is
arranged such that the frame portion has a first through-opening in
a junction where the frame portion connects to the arm portion, the
arm portion has, disposed on one face thereof, four of the strain
gauges consisting of a first strain gauge, a second strain gauge, a
third strain gauge, and a fourth strain gauge, the first strain
gauge and the second strain gauge are disposed in an area close to
the central portion such that (i) the first strain gauge and the
second strain gauge are symmetrical to each other with respect to a
center line of the one face, the center line extending in a
direction of extension of the arm portion, and (ii) detection
directions of the first strain gauge and the second strain gauge
are parallel to the center line, and the third strain gauge and the
fourth strain gauge are disposed in an area close to the frame
portion such that (i) the third strain gauge and the fourth strain
gauge are symmetrical to each other with respect to the center line
and (ii) detection directions of the third strain gauge and the
fourth strain gauge are at an angle to the center line so as to
diverge away from each other with decreasing distance to the
central portion.
[0190] According to an aspect of the present invention, the strain
element is arranged such that: the frame portion and the central
portion are connected by the arm portion; the frame portion has the
first through-opening facing the arm portion; the arm portion has,
disposed on one face thereof, the four strain gauges consisting of
a first strain gauge, a second strain gauge, a third strain gauge,
and a fourth strain gauge, the third strain gauge and the fourth
strain gauge are located in an area close to the frame portion such
that (i) the third strain gauge and the fourth strain gauge are
symmetrical to each other with respect to the center line in the
direction of extension of the arm portion and (ii) detection
directions of the third strain gauge and the fourth strain gauge
are at an angle to the center line so as to diverge away from each
other with decreasing distance to the central portion. Therefore,
in a case where an external force that causes moment in the
thickness direction of the strain element is exerted, the third
strain gauge and the fourth strain gauge, which are disposed at an
angle to the center line so as to diverge away from each other with
decreasing distance to the central portion, easily detect strain
associated with deformation that occurs when an external force is
exerted on the arm portion in the foregoing specific directions
(the foregoing Mz, Fx, and Fy directions). That is, the directions
at an angle to the center line, in which the third strain gauge and
the fourth strain gauge are disposed, are directions in which
strain associated with deformation that occurs when an external
force is exerted on the arm portion in the foregoing specific
directions is detected well. This makes it possible to ensure
highly sensitive measurement.
[0191] An aspect of the present invention includes: a frame
portion; a central portion which is located in a space defined by
the frame portion so as to be spaced apart from the frame portion;
and an arm portion which connects the frame portion with the
central portion and which corresponds to the strain portion, and is
arranged such that the central portion has (i) a locating
through-hole in an area corresponding to an extension of the arm
portion and (ii) a second through-opening located between the
locating through-hole and a junction where the central portion
connects to the arm portion.
[0192] According to an aspect of the present invention, the strain
element is arranged such that: the frame portion and the central
portion are connected by the arm portion; the central portion has
the locating through-hole; and there is the second through-opening
between the locating through-hole and the junction where the
central portion connects to the arm portion. Therefore, in the
region corresponding to an area of the central portion from which
the arm portion extends (in the region corresponding to the
junction where the central portion connects to the arm portion),
the vicinity of the locating through-hole increases in rigidity,
whereas the vicinity of the second through-opening has a relatively
low rigidity and is likely to flex. Because of this, the portion of
the arm portion where the arm portion connects to the central
portion is likely to elastically deform, and strain detection by
the strain gauge becomes easy. Accordingly, the accuracy of
measurement of values of physical quantities regarding external
forces and moments improves.
[0193] According to an aspect of the present invention, the strain
element is masked except for the strain portion, and then the shot
material is projected. As such, the shot material directly collides
with the strain portion. Because of such direct collision, a
residual stress layer having negative residual stress is formed in
the strain portion, and the strain portion is given a surface
roughness rougher than a portion other than the strain portion. The
residual stress layer results in an increase in resistance to
fatigue failure, and a physical quantity measurement sensor
including such a strain element can be used stably over a long
period of time. Furthermore, since the shot material directly
collides with the strain portion and thereby the strain portion is
given a surface roughness rougher than a portion other than the
strain portion, the strain gauge disposed on the strain portion
becomes better at conforming to deformation because of the anchor
effect provided by the adhesive, and the accuracy of strain
detection improves.
[0194] An aspect of the present invention is arranged such that the
strain element includes (i) a frame portion, (ii) a central portion
which is located in a space defined by the frame portion so as to
be spaced apart from the frame portion, and (iii) an arm portion
which connects the frame portion with the central portion and which
corresponds to the strain portion, and includes the step of corner
easing comprising easing (i) a corner of an edge of a junction
where the frame portion and the arm portion connect to each other
or (ii) a corner of an edge of a junction where the central portion
and the arm portion connect to each other.
[0195] According to an aspect of the present invention, in the
strain element configured such that the frame portion and the
central portion are connected by the arm portion, the corner at
which the frame portion and the arm portion connect to each other
or the corner at which the central portion and the arm portion
connect to each other is eased. This reduces stress concentration
that is likely to occur in such corners, and thereby further
increases the resistance to fatigue failure.
[0196] A physical quantity measurement sensor in accordance with an
aspect of the present invention includes the strain element
described above, and measures a physical quantity corresponding to
deformation of the strain element in response to a load.
[0197] According to an aspect of the present invention, a physical
quantity measurement sensor including the foregoing strain element
measures a physical quantity corresponding to deformation of the
strain element in response to a load. This makes it possible to
provide a physical quantity measurement sensor that maintains
stable, highly accurate measurement over a long period of time.
[0198] According to an aspect of the present invention, a residual
stress layer having compressive residual stress has been formed in
a strain portion. Therefore, the resistance to fatigue failure in
the portion that elastically deforms, in which the strain gauge
carries out detection, can be improved. This makes it possible to
achieve a long-term stable use of a physical quantity measurement
sensor in which the strain element in accordance with an aspect of
the present invention is employed.
[0199] According to an aspect of the present invention, the area
for attachment of the stain gauge has a large surface roughness.
Therefore, the strain gauge becomes better at conforming to the
elastic deformation of the strain element because of the anchor
effect provided by the adhesive. This makes it possible to achieve
stable measurement accuracy of a physical quantity measurement
sensor in which the strain element in accordance with an aspect of
the present invention is employed.
[0200] According to an aspect of the present invention, in the
strain element arranged such that the frame portion and the central
portion are connected by the arm portion and that the frame portion
has the first through-opening facing the arm portion, the third
strain gauge and the fourth strain gauge disposed on the arm
portion are disposed such that they are at an angle to the center
line so as to diverge away from each other with decreasing distance
to the central portion. This makes it possible to improve the
accuracy of detection of strain associated with elastic deformation
that occurs when an external force is exerted on the arm portion in
the foregoing specific directions (the foregoing Mz, Fx, and Fy
directions).
[0201] According to an aspect of the present invention, in the
strain element arranged such that the frame portion and the central
portion are connected by the arm portion, the locating through-hole
and the second through-opening have been formed corresponding to
the area of the central portion where the central portion connects
to the arm portion. This achieves a structure in which the portion
of the arm portion where the arm portion connects to the central
portion is likely to elastically deform in response to a load. This
makes it possible to increase measurement accuracy of a physical
quantity measurement sensor in which the strain element in
accordance with an aspect of the present invention is employed.
[0202] According to an aspect of the present invention, a shot
material is projected under the condition in which the strain
element is masked except for the strain portion. Therefore, a
residual stress layer can be formed in the strain portion which is
left unmasked. Furthermore, it is also possible to increase the
surface roughness of the strain portion. This makes it possible to
efficiently produce a strain element which is highly resistant to
fatigue failure and in which a strain gauge of a bonded type is
better at conforming to deformation because of the anchor effect
provided by the adhesive.
[0203] According to an aspect of the present invention, in the
strain element configured such that the frame portion and the
central portion are connected by the arm portion, a corner at which
the frame portion and the arm portion connect to each other or a
corner at which the central portion and the arm portion connect to
each other has been eased. This reduces stress concentration that
is likely to occur in such corners, and thereby further increases
the resistance to fatigue failure.
[0204] According to an aspect of the present invention, a physical
quantity measurement sensor including the foregoing strain element
measures a physical quantity corresponding to deformation of the
strain element in response to a load. This makes it possible to
ensure the condition in which stable, highly accurate measurement
is available over a long period of time.
INDUSTRIAL APPLICABILITY
[0205] The prevent invention is suitable for use in applications in
which a physical quantity measurement sensor including an
elastically deformable strain element increases the resistance to
fatigue failure and ensures long-term stable use.
REFERENCE SIGNS LIST
[0206] 1, 101 force sensor [0207] 2, 102 table block [0208] 6 base
block [0209] 10, 10', 10'', 55, 60, 70, 80, 90, 110 strain element
[0210] 11, 11', 11'', 71, 111 frame portion [0211] 12, 12', 12'',
72, 112 central portion [0212] 14a to 14c, 114a, 114b locating
through-hole [0213] 20 to 22, 20' to 22', 20'' to 22'', 73 to 76,
120 to 122 arm portion [0214] 25 to 27, 25'' to 27'', 125 to 127
through-opening [0215] 29 strain gauge circuit [0216] 30 signal
processing module [0217] 31 amplifier [0218] A-D converter [0219]
33 processor [0220] 34 memory [0221] 35 D-A converter [0222] 50' to
52', 50'' to 52'' near-center through-opening [0223] A1 to C4', A11
to C14' strain gauge
* * * * *